Zirconia sintered body having high linear light transmittance

ABSTRACT

A zirconia sintered body may excel in translucency, strength, and linear light transmittance with no use of an HIP device, and a zirconia molded body and a zirconia pre-sintered body from which such a zirconia sintered body can be obtained. A zirconia molded body may include zirconia particles with 2.0 to 9.0 mol % yttria, an average primary particle diameter of 60 nm or less, and 0.5 mass % or less zirconia particles having a particle diameter &gt;100 nm, wherein the zirconia molded body has ΔL*(W−B) of 5+ through a thickness of 1.5 mm. A zirconia pre-sintered body may include 2.0 to 9.0 mol % yttria, and have a ΔL*(W−B) of 5+ through a thickness of 1.5 mm. A zirconia sintered body may include: a fluorescent agent; 2.0 to 9.0 mol % yttria, and have a linear light transmittance of 1% or more through a thickness of 1.0 mm.

TECHNICAL FIELD

The present invention relates to a zirconia sintered body having highlinear light transmittance, among others.

BACKGROUND ART

A zirconia sintered body containing yttria has been used for dentalmaterials such as dental prostheses. Many of such dental prostheses areproduced by forming a zirconia molded body of a desired shape, forexample, a disc or prism shape, through the process of pressing zirconiaparticles or molding a slurry or a composition containing zirconiaparticles, followed by pre-sintering of the zirconia molded body into apre-sintered body (mill blank), and subsequent sintering of the zirconiapre-sintered body after cutting (milling) it into the shape of thedesired dental prosthesis.

It has been confirmed that linear light transmittance improves byreducing and uniformizing the crystal grain size of a zirconia sinteredbody (see, for example, Patent Literature 1). To reduce and uniformizethe crystal grain size of a zirconia sintered body, hot isostaticpressing (HIP) treatment is required. However, since an HIP device usedfor the HIP treatment is a special device classified as a high-pressuregas generator, it is difficult to say that a zirconia sintered bodyhaving high linear light transmittance can be obtained with ease.

CITATION LIST Patent Literature

Patent Literature 1: JP 2008-214168 A

SUMMARY OF INVENTION Technical Problem

It is an object of the present invention to provide a zirconia sinteredbody that excels in both strength and translucency and excels in linearlight transmittance with no use of an HIP device. Another object of thepresent invention is to provide a zirconia molded body and a zirconiapre-sintered body from which such a zirconia sintered body can beobtained, and methods for conveniently producing these.

Solution to Problem

The present inventors conducted intensive studies to achieve theforegoing objects, and found that a zirconia sintered body that excelsin linear light transmittance can be obtained with no use of an HIPdevice, by sintering under ordinary pressure a zirconia molded body thatincludes zirconia particles having an average particle diameter of 60 nmor less and including 0.5 mass % or less zirconia particles having aparticle diameter of more than 100 nm, and has ΔL*(W−B) of 5 or morethrough a thickness of 1.5 mm. It was also found that the novel zirconiasintered body is particularly preferred as, for example, dentalmaterials such as dental prostheses, and is highly useful not only as adental prosthesis used for the cervical region of a tooth but as adental prosthesis used for the occlusal surface of a posterior tooth,and the incisal region of a front tooth. The present inventors completedthe present invention after further studies based on these findings.

Specifically, the present invention relates to the following [1] to[19].

-   [1] A zirconia molded body comprising zirconia particles comprising    2.0 to 9.0 mol % yttria, having an average primary particle diameter    of 60 nm or less, and including 0.5 mass % or less zirconia    particles having a particle diameter of more than 100 nm, wherein    the zirconia molded body has ΔL*(W−B) of 5 or more through a    thickness of 1.5 mm.-   [2] The zirconia molded body according to [1], wherein the zirconia    molded body has a three-point flexural strength of 500 MPa or more    after being sintered at 900 to 1,200° C. under ordinary pressure.-   [3] The zirconia molded body according to [1] or [2], wherein the    zirconia molded body has a transmittance of 40% or more for light of    700 nm wavelength through a thickness of 0.5 mm after being sintered    at 900 to 1,200° C. under ordinary pressure.-   [4] The zirconia molded body according to any one of [1] to [3],    wherein the zirconia molded body comprises a monoclinic crystal    system in a fraction of 5% or less with respect to a tetragonal    crystal system and a cubic crystal system after being sintered at    900 to 1,200° C. under ordinary pressure and then immersed in    180° C. hot water for 5 hours.-   [5] The zirconia molded body according to any one of [1] to [4],    wherein the zirconia molded body has ΔL*(W−B) of 5 or more through a    thickness of 1.5 mm after being sintered at 200 to 800° C.-   [6] A zirconia pre-sintered body comprising 2.0 to 9.0 mol % yttria,    wherein the zirconia pre-sintered body has ΔL*(W−B) of 5 or more    through a thickness of 1.5 mm.-   [7] The zirconia pre-sintered body according to [6], wherein the    zirconia pre-sintered body has a three-point flexural strength of    500 MPa or more after being sintered at 900 to 1,200° C. under    ordinary pressure.-   [8] The zirconia pre-sintered body according to [6] or [7], wherein    the zirconia pre-sintered body has a transmittance of 40% or more    for light of 700 nm wavelength through a thickness of 0.5 mm after    being sintered at 900 to 1,200° C. under ordinary pressure.-   [9] The zirconia pre-sintered body according to any one of [6] to    [8], wherein the zirconia pre-sintered body comprises a monoclinic    crystal system in a fraction of 5% or less with respect to a    tetragonal crystal system and a cubic crystal system after being    sintered at 900 to 1,200° C. under ordinary pressure and then    immersed in 180° C. hot water for 5 hours.-   [10] A method for producing a zirconia pre-sintered body, wherein    the method uses the zirconia molded body of any one of [1] to [5].-   [11] The method according to [10], comprising a step of    pre-sintering the zirconia molded body of any one of [1] to [5] at    200 to 800° C.-   [12] A zirconia sintered body comprising: a fluorescent agent; and    2.0 to 9.0 mol % yttria, wherein the zirconia sintered body has a    linear light transmittance of 1% or more through a thickness of 1.0    mm.-   [13] The zirconia sintered body according to [12], wherein the    zirconia sintered body has a three-point flexural strength of 500    MPa or more.-   [14] The zirconia sintered body according to [12] or [13], wherein    the zirconia sintered body has a transmittance of 40% or more for    light of 700 nm wavelength through a thickness of 0.5 mm.-   [15] The zirconia sintered body according to any one of [12] to    [14], wherein the zirconia sintered body comprises a monoclinic    crystal system in a fraction of 5% or less with respect to a    tetragonal crystal system and a cubic crystal system after being    immersed in 180° C. hot water for 5 hours.-   [16] A method for producing a zirconia sintered body, wherein the    method uses the zirconia molded body of any one of [1] to [5].-   [17] The method according to [16], comprising a step of sintering    the zirconia molded body at 900 to 1,200° C. under ordinary    pressure.-   [18] A method for producing a zirconia sintered body, wherein the    method uses the zirconia pre-sintered body of any one of [6] to [9].-   [19] The method according to [18], comprising a step of sintering    the zirconia pre-sintered body at 900 to 1,200° C. under ordinary    pressure.

Advantageous Effects of Invention

According to the present invention, a zirconia sintered body is providedthat excels in both translucency and strength and excels in linear lighttransmittance, with no use of an HIP device. A zirconia molded body anda zirconia pre-sintered body are also provided from which such azirconia sintered body can be obtained. The present invention alsoprovides methods for conveniently producing these.

DESCRIPTION OF EMBODIMENTS

The present invention includes a zirconia molded body comprisingzirconia particles comprising 2.0 to 9.0 mol % yttria (Y₂O₃), having anaverage primary particle diameter of 60 nm or less, and including 0.5mass % or less zirconia particles having a particle diameter of morethan 100 nm, wherein the zirconia molded body has ΔL*(W−B) of 5 or morethrough a thickness of 1.5 mm. With use of the zirconia molded body, itis possible to obtain a zirconia sintered body that excels in bothtranslucency and strength and excels in linear light transmittance. Thepresent invention also includes a zirconia pre-sintered body comprising2.0 to 9.0 mol % yttria, wherein the zirconia pre-sintered body hasΔL*(W−B) of 5 or more through a thickness of 1.5 mm. With use of thezirconia pre-sintered body, the zirconia sintered body can also beobtained. The following firstly describes a zirconia sintered body as anembodiment of the present invention. A zirconia sintered body of thepresent invention comprises: a fluorescent agent; and 2.0 to 9.0 mol %yttria, wherein the zirconia sintered body has a linear lighttransmittance of 1% or more through a thickness of 1.0 mm. It is to benoted that the following descriptions do not limit the presentinvention.

Zirconia Sintered Body

A zirconia sintered body of the present invention comprises afluorescent agent. By containing a fluorescent agent, the zirconiasintered body exhibits fluorescence. The type of fluorescent agent isnot particularly limited, and the fluorescent agent may be one or morefluorescent agents capable of emitting fluorescence under the light ofany wavelength. Examples of such fluorescent agents include thosecontaining metallic elements. Examples of the metallic elements includeGa, Bi, Ce, Nd, Sm, Eu, Gd, Tb, Dy, and Tm. The fluorescent agent maycontain one of these metallic elements alone, or may contain two or moreof these metallic elements. For advantages such as enhancing the effectsof the present invention, the metallic elements are preferably Ga, Bi,Eu, Gd, and Tm, more preferably Bi and Eu. The fluorescent agent used toproduce the zirconia sintered body of the present invention may be, forexample, an oxide, hydroxide, acetate, or nitrate of the metallicelements above. The fluorescent agent may be, for example, Y₂SiO₅:Ce,Y₂SiO₅:Tb, (Y,Gd,Eu)BO₃, Y₂O₃:Eu, YAG:Ce, ZnGa₂O₄:Zn, or BaMgAl₁₀O₁₇:Eu.

The content of the fluorescent agent in the zirconia sintered body isnot particularly limited, and may be appropriately adjusted according tosuch factors as the type of fluorescent agent, and the use of thezirconia sintered body. However, for advantages such as suitability asdental prostheses, the fluorescent agent content is preferably 0.001mass % or more, more preferably 0.005 mass % or more, even morepreferably 0.01 mass % or more, and is preferably 1 mass % or less, morepreferably 0.5 mass % or less, even more preferably 0.1 mass % or lessin terms of an oxide of the metallic element contained in thefluorescent agent, relative to the mass of the zirconia contained in thezirconia sintered body. With the fluorescent agent contained in anamount equal to or greater than these lower limits, the zirconiasintered body can produce fluorescence comparable to that of naturalhuman teeth. With the fluorescent agent contained in an amount equal toor less than the foregoing upper limits, decrease of translucency andstrength can be reduced.

The zirconia sintered body of the present invention may contain acolorant. By containing a colorant, the zirconia sintered body can havea color. The type of colorant is not particularly limited, and thecolorant may be a known pigment commonly used to color ceramics, or aknown dental liquid colorant. Examples of the colorant include colorantscontaining metallic elements, specifically, oxides, composite oxides,and salts containing metallic elements such as iron, vanadium,praseodymium, erbium, chromium, nickel, and manganese. The colorant maybe a commercially available colorant, for example, such as the PrettauColour Liquid manufactured by Zirkonzahn. The zirconia sintered body maycontain one kind of colorant, or may contain two or more kinds ofcolorants.

The content of the colorant in the zirconia sintered body is notparticularly limited, and may be appropriately adjusted according tosuch factors as the type of colorant, and the use of the zirconiasintered body. However, for advantages such as suitability as dentalprostheses, the colorant content is preferably 0.001 mass % or more,more preferably 0.005 mass % or more, even more preferably 0.01 mass %or more, and is preferably 5 mass % or less, more preferably 1 mass % orless, even more preferably 0.5 mass % or less, and may be 0.1 mass % orless, or 0.05 mass % or less in terms of an oxide of the metallicelement contained in the colorant, relative to the mass of the zirconiacontained in the zirconia sintered body.

With the present invention, a zirconia sintered body having high linearlight transmittance can be obtained. The zirconia sintered body of thepresent invention may contain a translucency adjuster for adjustment oftranslucency in the zirconia sintered body. Specific examples of thetranslucency adjuster include aluminum oxide, titanium oxide, silicondioxide, zircon, lithium silicate, and lithium disilicate. The zirconiasintered body may contain one kind of translucency adjuster, or maycontain two or more kinds of translucency adjusters.

The content of the translucency adjuster in the zirconia sintered bodyis not particularly limited, and may be appropriately adjusted accordingto such factors as the type of translucency adjuster, and the use of thezirconia sintered body. However, for advantages such as suitability asdental prostheses, the content of translucency adjuster is preferably0.1 mass % or less relative to the mass of the zirconia contained in thezirconia sintered body.

The zirconia sintered body of the present invention contains 2.0 to 9.0mol % yttria. The zirconia sintered body cannot have sufficienttranslucency with an yttria content of less than 2.0 mol %. The strengthdecreases when the yttria content in the zirconia sintered body is morethan 9.0 mol %. For advantages such as producing a zirconia sinteredbody having improved translucency and strength, the yttria content inthe zirconia sintered body is preferably 3.0 mol % or more, morepreferably 4.0 mol % or more, and is preferably 8.0 mol % or less, morepreferably 7.0 mol % or less. It is to be noted that the yttria contentin the zirconia sintered body is a fraction (mol %) of the number ofmoles of yttria with respect to the total number of moles of zirconiaand yttria.

The zirconia sintered body of the present invention has a crystal grainsize of preferably 180 nm or less. Insufficient translucency might beobtained with a crystal grain size of more than 180 nm. For advantagessuch as producing a zirconia sintered body having improved translucency,the crystal grain size is preferably 140 nm or less, more preferably 120nm or less, even more preferably 110 nm or less, and may be 100 nm orless. The lower limit of crystal grain size is not particularly limited,and the crystal grain size may be, for example, 50 nm or more, or 70 nmor more. The crystal grain size of the zirconia sintered body can bedetermined by taking a micrograph of zirconia sintered body crosssections with a field emission scanning electron microscope (FE-SEM),and finding a mean value of diameters of circles corresponding to 10arbitrarily selected particles from the micrograph (the diameters oftrue circles having the same areas as these particles).

The zirconia sintered body of the present invention excels in strength.The zirconia sintered body of the present invention has a three-pointflexural strength of 500 MPa or more, preferably 600 MPa or more, morepreferably 650 MPa or more, even more preferably 700 MPa or more,particularly preferably 800 MPa or more. With the three-point flexuralstrength falling in these ranges, the zirconia sintered body of thepresent invention can have a reduced chance of breaking or fracturing inthe mouth when used as, for example, a dental prosthesis. The upperlimit of three-point flexural strength is not particularly limited, andthe three-point flexural strength may be, for example, 1,500 MPa orless, or 1,000 MPa or less. The three-point flexural strength ofzirconia sintered body can be measured in compliance with ISO 6872:2015.

The zirconia sintered body of the present invention excels intranslucency. The zirconia sintered body of the present invention has atransmittance of preferably 40% or more, more preferably 45% or more,and may have a transmittance of 46% or more, 48% or more, 50% or more,or 52% or more for light of 700 nm wavelength through a thickness of 0.5mm. With the transmittance falling in these ranges, the zirconiasintered body can more easily satisfy the level of translucency requiredfor the incisal region when used as, for example, a dental prosthesis.The upper limit of transmittance is not particularly limited, and thetransmittance may be, for example, 60% or less, or 57% or less. Thetransmittance of zirconia sintered body for light of 700 nm wavelengththrough a thickness of 0.5 mm may be measured with a spectrophotometer.For example, the transmittance can be measured with an integratingsphere by measuring light from a light source passing and scattering ona specimen, using a spectrophotometer (Hitachi spectrophotometer, ModelU-3900H manufactured by Hitachi High-Technologies Corporation). In themeasurement, the transmittance for light of 700 nm wavelength may bedetermined after measuring transmittance in a wavelength region of 300to 750 nm. The specimen used for measurement may be a disc-shapedzirconia sintered body having mirror polished surfaces and measuring 15mm in diameter and 0.5 mm in thickness.

The zirconia sintered body of the present invention excels in linearlight transmittance. It is important for the zirconia sintered body ofthe present invention to have a linear light transmittance of 1% or morethrough a thickness of 1.0 mm. The linear light transmittance ispreferably 3% or more, more preferably 5% or more, even more preferably7% or more, and may be 10% or more. With the linear light transmittancefalling in these ranges, the zirconia sintered body can more easilysatisfy the level of translucency required for the incisal region whenused as, for example, a dental prosthesis. The upper limit of linearlight transmittance is not particularly limited, and the linear lighttransmittance may be, for example, 60% or less, or 50% or less. Thelinear light transmittance of zirconia sintered body through a thicknessof 1.0 mm may be measured with a turbidimeter. For example, the linearlight transmittance can be measured with an integrating sphere bymeasuring light from a light source passing and scattering on aspecimen, using a turbidimeter (Haze Meter NDH 4000 manufactured byNippon Denshoku Industries Co., Ltd.). In the measurement, the linearlight transmittance is measured preferably in compliance with ISO13468-1:1996 and JIS K 7361-1:1997, and the haze is measured preferablyin compliance with ISO 14782-1:1999 and JIS K 7136:2000. The specimenused for measurement may be a disc-shaped zirconia sintered body havingmirror polished surfaces and measuring 15 mm in diameter and 1.0 mm inthickness.

The predominant crystal phase of the zirconia sintered body of thepresent invention may be a tetragonal crystal system or a cubic crystalsystem. However, a fraction of the cubic crystal system in the zirconiasintered body is preferably higher than that of the tetragonal crystalsystem. The zirconia sintered body of the present invention ispreferably at least 30% cubic crystal system, more preferably at least50% cubic crystal system. The fraction of the cubic crystal system inthe zirconia sintered body may be determined by crystal phase analysis.Specifically, the fraction of the cubic crystal system may be determinedby X-ray diffraction (XRD) analysis of a mirror finished surface portionof the zirconia sintered body, using the following formula.

f _(c)=100×I _(c)/(I _(m) +I _(t) +I _(c))

Here, f_(c) represents the fraction (%) of the cubic crystal system inthe zirconia sintered body, I_(m) represents the height of a peak (apeak attributed to the (11-1) plane of a monoclinic crystal system) near2θ=28 degrees, I_(t) represents the height of a peak (a peak attributedto the (111) plane of a tetragonal crystal system) near 2θ=30 degrees,and I_(c) represents the height of a peak (a peak attributed to the(111) plane of the cubic crystal system) near 2θ=30 degrees. When thepeak near 2θ=30 degrees appears as a peak attributed to a mixed phase ofthe (111) plane of the tetragonal crystal system and the (111) plane ofthe cubic crystal system, and separation is difficult to achieve for thepeak attributed to the (111) plane of the tetragonal crystal system andthe peak attributed to the (111) plane of the cubic crystal system,I_(t) and I_(c) can be determined by determining the ratio of tetragonalcrystal and cubic crystal system using a technique such as the Rietveldmethod, and then multiplying the ratio by the height (I_(t+c)) of thepeak attributed to the mixed phase.

In the zirconia sintered body of the present invention, the fraction ofmonoclinic crystal system with respect to tetragonal crystal system andcubic crystal system after the zirconia sintered body is immersed in180° C. hot water for 5 hours is preferably 5% or less, more preferably3% or less, even more preferably 1% or less. With the fraction fallingin these ranges, volume changes due to aging can be reduced, andbreakage can be prevented when the zirconia sintered body is used as,for example, a dental prosthesis. The fraction can be determined bymirror polishing a surface of the zirconia sintered body, and measuringthe mirror polished surface portion by X-ray diffraction (XRD) analysisafter the zirconia sintered body is immersed in 180° C. hot water for 5hours, using the following formula.

f _(m)=100×I _(m)/(I _(t+c))

Here, f_(m) represents the fraction (%) of the monoclinic crystal systemwith respect to the tetragonal crystal system and the cubic crystalsystem in the zirconia sintered body immersed in 180° C. hot water for 5hours, Int represents the height of a peak (a peak attributed to the(11-1) plane of the monoclinic crystal) near 2θ=28 degrees, and I_(t+c)represents the height of a peak (a peak attributed to a mixed phase ofthe (111) plane of the tetragonal crystal system and the (111) plane ofthe cubic crystal system) near 2θ=30 degrees. When I_(t+c) cannot beeasily specified as a result of the peak near 2θ=30 degrees separatelyappearing as a peak attributed to the (111) plane of the tetragonalcrystal system and a peak attributed to the (111) plane of the cubiccrystal system, I_(t+c) can be determined as the sum of the height(I_(t)) of the peak attributed to the (111) plane of the tetragonalcrystal system and the height (I_(c)) of the peak attributed to the(111) plane of the cubic crystal system.

The method of production of the zirconia sintered body of the presentinvention is characterized by using the zirconia molded body of thepresent invention described below, and preferably includes a step ofsintering the zirconia molded body at 900 to 1,200° C. under ordinarypressure. Alternatively, the method of production of the zirconiasintered body of the present invention may use the zirconia pre-sinteredbody of the present invention described below, and preferably includes astep of sintering the zirconia pre-sintered body at 900 to 1,200° C.under ordinary pressure. With these producing methods, it is possible toeasily produce the zirconia sintered body of the present invention thatexcels in both translucency and strength and excels in linear lighttransmittance.

Zirconia Molded Body

The zirconia molded body of the present invention is characterized bycomprising zirconia particles comprising 2.0 to 9.0 mol % yttria (Y₂O₃),having an average primary particle diameter of 60 nm or less, andincluding 0.5 mass % or less zirconia particles having a particlediameter of more than 100 nm, wherein the zirconia molded body hasΔL*(W−B) of 5 or more through a thickness of 1.5 mm. With use of thezirconia molded body, it is possible to obtain a zirconia sintered bodythat excels in both translucency and strength and excels in linear lighttransmittance.

The zirconia molded body of the present invention has high translucency.It is possible to produce, from such a zirconia molded body, a zirconiasintered body having high linear light transmittance and a zirconiapre-sintered body from which a zirconia sintered body having high linearlight transmittance can be produced. Specifically, it is important forthe zirconia molded body of the present invention to have ΔL*(W−B) of 5or more through a thickness of 1.5 mm. The ΔL*(W−B) is preferably 8 ormore, more preferably 10 or more. Here, ΔL*(W−B) indicates thedifference between lightness on a white background (L*) and lightness ona black background (L*). Specifically, ΔL*(W−B) indicates the differencebetween an L* value on the white background and an L* value on the blackbackground (JIS Z 8781-4: 2013 colorimetry-Part 4: CIE 1976 L*, a*, b*,color space). The white background and the black background respectivelyindicate a white part and a black part on a hiding-chart specified inJIS K 5600-4-1: 1999, Part 4, Section 1. With the ΔL*(W−B) in the rangeas above, a zirconia sintered body having high linear lighttransmittance can be obtained after being sintered under ordinarypressure. The upper limit of ΔL*(W−B) is not particularly limited. Forexample, the ΔL*(W−B) may be 30 or less, or from the viewpoint ofesthetic quality, may be 25 or less. The ΔL*(W−B) of zirconia moldedbody through a thickness of 1.5 mm may be measured with aspectrophotometer. For example, the ΔL*(W−B) can be measured with aspectrophotometer (CM-3610A manufactured by Konica Minolta Japan, Inc.,geometric condition c (di: 8°, de: 8°), diffuse illumination: 8° lightreception, measurement mode SCI, measurement diameter/illuminationdiameter=φ8 mm/φ11 mm), and calculated with color management softwareSpectraMagic NX ver. 2.5 manufactured by Konica Minolta Co., Ltd. In themeasurement, the ΔL*(W−B) may be determined by using F11 as a lightsource. The specimen used for measurement may be a disc-shaped zirconiamolded body measuring 20 mm in diameter and 1.5 mm in thickness.

When producing a zirconia sintered body containing a fluorescent agent,it is preferable that the fluorescent agent be contained in the zirconiamolded body. The content of the fluorescent agent in the zirconia moldedbody of the present invention may be appropriately adjusted accordingto, for example, the content of the fluorescent agent in the zirconiasintered body to be produced. Specifically, the content of thefluorescent agent in the zirconia molded body is preferably 0.001 mass %or more, more preferably 0.005 mass % or more, even more preferably 0.01mass % or more, and is preferably 1 mass % or less, more preferably 0.5mass % or less, even more preferably 0.1 mass % or less in terms of anoxide of the metallic element contained in the fluorescent agent,relative to the mass of the zirconia contained in the zirconia moldedbody.

When producing a zirconia sintered body containing a colorant, it ispreferable that the colorant be contained in the zirconia molded body.The content of the colorant in the zirconia molded body of the presentinvention may be appropriately adjusted according to, for example, thecontent of the colorant in the zirconia sintered body to be produced.Specifically, the content of the colorant in the zirconia molded body ispreferably 0.001 mass % or more, more preferably 0.005 mass % or more,even more preferably 0.01 mass % or more, and is preferably 5 mass % orless, more preferably 1 mass % or less, even more preferably 0.5 mass %or less, and may be 0.1 mass % or less, or 0.05 mass % or less in termsof an oxide of the metallic element contained in the colorant, relativeto the mass of the zirconia contained in the zirconia molded body.

When producing a zirconia sintered body containing a translucencyadjuster, it is preferable that the translucency adjuster be containedin the zirconia molded body. The content of the translucency adjuster inthe zirconia molded body of the present invention may be appropriatelyadjusted according to, for example, the content of the translucencyadjuster in the zirconia sintered body to be produced. Specifically, thecontent of the translucency adjuster in the zirconia molded body ispreferably 0.1 mass % or less relative to the mass of the zirconiacontained in the zirconia molded body.

The yttria content in the zirconia molded body of the present inventionmay be the same as the yttria content in the zirconia sintered body tobe produced, within a range of 2.0 to 9.0 mol %. Specifically, theyttria content in the zirconia molded body is 2.0 mol % or more,preferably 3.0 mol % or more, more preferably 4.0 mol % or more, and is9.0 mol % or less, preferably 8.0 mol % or less, more preferably 7.0 mol% or less. It is to be noted that the yttria content in the zirconiamolded body is a fraction (mol %) of the number of moles of yttria withrespect to the total number of moles of zirconia and yttria.

The density of the zirconia molded body of the present invention is notparticularly limited, and varies with factors such as the method ofproduction of the zirconia molded body. However, for advantages such asproducing a more compact zirconia sintered body, the density ispreferably 3.0 g/cm³ or more, more preferably 3.2 g/cm³ or more, evenmore preferably 3.4 g/cm³ or more. The upper limit of density is notparticularly limited, and may be, for example, 6.0 g/cm³ or less, or 5.8g/cm³ or less.

The shape of the zirconia molded body of the present invention is notparticularly limited, and may be chosen as desired according to use.However, for example, considering ease of handing of when producing azirconia pre-sintered body to be used as a mill blank for producing adental material such as a dental prosthesis, the zirconia molded bodypreferably has a disc or a prism shape (e.g., rectangular). By using atechnique such as stereolithography, a shape corresponding to the shapedesired for the product zirconia sintered body can be imparted to thezirconia molded body during its production, as will be described later.The present invention also encompasses zirconia molded bodies havingsuch desired shapes. The zirconia molded body may have a monolayerstructure or a multilayer structure. With a multilayered zirconia moldedbody, the resulting zirconia sintered body can have a multilayerstructure, which allows translucency and other physical properties to belocally altered.

For considerations such as ease of handling, the zirconia molded body ofthe present invention has a biaxial flexural strength in a range ofpreferably 2 to 10 MPa, more preferably 5 to 8 MPa. The biaxial flexuralstrength of zirconia molded body can be measured in compliance with JIST 6526:2018.

The zirconia molded body of the present invention has a crystal grainsize of preferably 180 nm or less after being sintered at 900 to 1,200°C. for 2 hours under ordinary pressure (after being formed into azirconia sintered body). In this way, the zirconia sintered body of thepresent invention having excellent translucency can be produced withease. For advantages such as producing a zirconia sintered body havingeven higher translucency, the crystal grain size is more preferably 140nm or less, even more preferably 120 nm or less, further even morepreferably 110 nm or less, and may be 100 nm or less. The lower limit ofcrystal grain size is not particularly limited, and the crystal grainsize may be, for example, 50 nm or more, or 70 nm or more. Here, thecrystal grain size is a measured value obtained in the same manner as inthe crystal grain size measurement described above in conjunction withthe zirconia sintered body.

The zirconia molded body of the present invention has a three-pointflexural strength of preferably 500 MPa or more after being sintered at900 to 1,200° C. under ordinary pressure (after being formed into azirconia sintered body). In this way, the zirconia sintered body of thepresent invention having excellent strength can be produced with ease.For advantages such as producing a zirconia sintered body having evenhigher strength, the three-point flexural strength is more preferably600 MPa or more, even more preferably 650 MPa or more, further even morepreferably 700 MPa or more, particularly preferably 800 MPa or more. Theupper limit of three-point flexural strength is not particularlylimited, and the three-point flexural strength may be, for example,1,500 MPa or less, or 1,000 MPa or less. Here, the three-point flexuralstrength is a measured value obtained in the same manner as in thethree-point flexural strength measurement described above in conjunctionwith the zirconia sintered body.

The zirconia molded body of the present invention has a transmittance ofpreferably 40% or more for light of 700 nm wavelength through athickness of 0.5 mm after being sintered at 900 to 1,200° C. underordinary pressure (after being formed into a zirconia sintered body). Inthis way, the zirconia sintered body of the present invention havingexcellent translucency can be produced with ease. For advantages such asproducing a zirconia sintered body having even higher translucency, thetransmittance is more preferably 45% or more, even more preferably 46%or more, further even more preferably 48% or more, particularlypreferably 50% or more, and may be 52% or more. The upper limit oftransmittance is not particularly limited, and the transmittance may be,for example, 60% or less, or 57% or less. Here, the transmittance is ameasured value obtained in the same manner as in the measurement oftransmittance for light of 700 nm wavelength through a thickness of 0.5mm described above in conjunction with the zirconia sintered body.

The zirconia molded body of the present invention has a linear lighttransmittance of preferably 1% or more, more preferably 3% or more, evenmore preferably 5% or more, further even more preferably 7% or more, andmay be 10% or more, through a thickness of 1.0 mm after being sinteredat 900 to 1,200° C. under ordinary pressure (after being formed into azirconia sintered body). With the linear light transmittance falling inthese ranges, the zirconia sintered body can more easily satisfy thelevel of translucency required for the incisal region when used as, forexample, a dental prosthesis. The upper limit of linear lighttransmittance is not particularly limited, and the linear lighttransmittance may be, for example, 60% or less, or 50% or less. Thelinear light transmittance can be measured in the same manner as in themeasurement of linear light transmittance through a thickness of 1.0 mmdescribed above in conjunction with the zirconia sintered body.

Method of Production of Zirconia Molded Body

The method of production of the zirconia molded body of the presentinvention is not particularly limited as long as the effects of thepresent invention are exhibited. However, for easy production of thezirconia sintered body of the present invention that excels in bothtranslucency and strength and excels in linear light transmittance, themethod of production of the zirconia molded body of the presentinvention is preferably a method that includes a molding step of moldingzirconia particles.

The yttria content in the zirconia particles used is preferably the sameas the yttria content in the zirconia molded body, and, in turn, theyttria content in the zirconia pre-sintered body and the zirconiasintered body to be produced. Specifically, the yttria content in thezirconia particles is preferably 2.0 mol % or more, more preferably 3.0mol % or more, even more preferably 4.0 mol % or more, and is preferably9.0 mol % or less, more preferably 8.0 mol % or less, even morepreferably 7.0 mol % or less. It is to be noted that the yttria contentin the zirconia particles is a fraction (mol %) of the number of molesof yttria with respect to the total number of moles of zirconia andyttria.

It is important that the zirconia particles have an average primaryparticle diameter of 60 nm or less, and the content of zirconiaparticles having a particle diameter of more than 100 nm is 0.5 mass %or less with respect to the total amount of the zirconia particles, in aparticle size distribution. In this way, the zirconia molded body of thepresent invention, and, in turn, the zirconia pre-sintered body and thezirconia sintered body of the present invention can be obtained withease. For considerations such as ease of production of the zirconiamolded body of the present invention, and, in turn, the zirconiapre-sintered body and the zirconia sintered body of the presentinvention, the average primary particle diameter of the zirconiaparticles included in the resulting zirconia molded body is preferably50 nm or less, more preferably 30 nm or less, even more preferably 20 nmor less, and may be 10 nm or less, and is preferably 1 nm or more, morepreferably 5 nm or more. For considerations such as ease of productionof the zirconia molded body of the present invention, and, in turn, thezirconia pre-sintered body and the zirconia sintered body of the presentinvention, and ease of obtaining a desired linear light transmittance,zirconia particles having a particle diameter of more than 100 nm arepreferably 0.3 mass % or less, more preferably 0.1 mass % or less, andmay be 0.05 mass % or less. The average primary particle diameter ofzirconia particles can be determined by, for example, taking amicrograph of zirconia particles (primary particles) with a transmissionelectron microscope (TEM), and finding a mean value of particlediameters (maximum diameters) measured for arbitrarily chosen 100particles from the photographed image. The content of the zirconiaparticles having a particle diameter of more than 100 nm may be measuredwith for example a zeta potential measurement device (for example, areal-time zeta potential/nanoparticle size measurement device (DelsaMaxPRO under trade name manufactured by Beckman Coulter Co., Ltd.) or azeta potential/particle size/molecular weight measurement system(ELSZ-2000ZS under trade name manufactured by Otsuka Electronics Co.,Ltd.)). For example, both amounts of zirconia particles before and afterparticle classification are measured, and an amount of zirconiaparticles having a particle diameter differing between the measuredvalues (mass %) by more than 100 nm corresponds to the content ofzirconia particles having a particle diameter of more than 100 nm.

The method of preparation of zirconia particles is not particularlylimited, and the zirconia particles may be prepared by using, forexample, a breakdown process that pulverizes coarse particles into afine powder, or a building-up process that synthesizes particles throughnucleation and nuclear growth from atoms and ions. The building-upprocess is more preferred for obtaining high-purity, fine zirconiaparticles.

The breakdown process may use, for example, a ball mill or bead mill forpulverization. Here, it is preferable to use microsize pulverizationmedia, for example, pulverization media of 100 μm or less. Also, fromthe viewpoint of obtaining desired ΔL*(W−B) and linear lighttransmittance, it is preferable to classify the zirconia particlesobtained after pulverization of coarse particles. Classification may beperformed with known methods and devices, such as porous membranes(membrane filters having a pore diameter of 100 nm) and classifiers (wetclassifier and dry classifier).

The building-up process may be, for example, vapor-phase pyrolysis,which is a process by which an oxoacid salt of high-vapor-pressure metalions, or a high-vapor-pressure organometallic compound is decomposedunder heat through vaporization to precipitate an oxide; vapor-phasereaction, which synthesizes particles through vapor-phase chemicalreaction of a high-vapor-pressure metallic compound gas with a reactivegas; evaporative concentration, in which a feedstock material is heatedto evaporate, and cooled rapidly in an inert gas of a predeterminedpressure to condense the steam into a fine particle form; a melt processthat forms a powder by cooling and solidifying small liquid droplets ofmelt; solvent evaporation, which causes precipitation in asupersaturated state created by increasing the concentration byevaporating the solvent in a solution; or a precipitation process inwhich the solute concentration is brought to a supersaturated statethrough reaction with a precipitating agent or hydrolysis, and a poorlysoluble compound such as an oxide and hydroxide is precipitated throughnucleation and nuclear growth.

The precipitation process can be sub-divided into processes thatinclude: homogenous precipitation in which a precipitating agent isgenerated in a solution by chemical reaction to eliminate localheterogeneity in the concentration of precipitating agent;coprecipitation in which a plurality of metal ions coexisting in asolution is simultaneously precipitated by addition of a precipitatingagent; a hydrolysis process that produces an oxide or hydroxide throughhydrolysis from a metal salt solution, an alcohol solution of metalalkoxide or the like; and solvothermal synthesis that produces an oxideor hydroxide from a high-temperature high-pressure fluid. Thesolvothermal synthesis is further divided into processes that includehydrothermal synthesis that uses water as solvent, and supercriticalsynthesis that uses a supercritical fluid such as water or carbondioxide as solvent.

Regardless of the building-up process, it is preferable to increase theprecipitation rate to obtain finer zirconia particles. Also, from theviewpoint of obtaining desired ΔL*(W−B) and linear light transmittance,it is preferable to classify the zirconia particles obtained.Classification may be performed with known methods and devices, such asporous membranes (membrane filters having a pore diameter of 100 nm) andclassifiers (wet classifier and dry classifier).

The zirconium source in the building-up process may be, for example,nitrate, acetate, chloride, or alkoxide. Specifically, for example,zirconium oxychloride, zirconium acetate, and zirconyl nitrate may beused.

In order to achieve the foregoing yttria content ranges in the zirconiaparticles, yttria may be added in the process of producing zirconiaparticles. For example, a solid solution of yttria may be formed inzirconia particles. The yttrium source may be, for example, nitrate,acetate, chloride, or alkoxide. Specifically, for example, yttriumchloride, yttrium acetate, and yttrium nitrate may be used.

As required, the zirconia particles may be subjected to a surfacetreatment in advance with a known surface treatment agent selected from,for example, organic compounds having acidic groups; fatty acid amidessuch as saturated fatty acid amides, unsaturated fatty acid amides,saturated fatty acid bisamides, and unsaturated fatty acid bisamides;and organometallic compounds such as silane coupling agents(organosilicon compounds), organic titanium compounds, organic zirconiumcompounds, and organic aluminum compounds. A surface treatment ofzirconia particles allows for adjustments of miscibility with a liquidhaving a surface tension at 25° C. of 50 mN/m or less when such a liquidis contained in the dispersion medium of a slurry used when preparing azirconia particle- and fluorescent agent-containing powder, as will bedescribed later. A surface treatment also allows the zirconia particlesto have adjusted miscibility with a polymerizable monomer, for example,when producing the zirconia molded body using a method that includespolymerizing a composition containing zirconia particles, a fluorescentagent, and a polymerizable monomer, as will be described later. Thesurface treatment agent is preferably an organic compound having anacidic group because of advantages such as desirable miscibility with aliquid having a surface tension at 25° C. of 50 mN/m or less, and theability to increase the strength of the resulting zirconia molded bodyby improving the chemical bonding between the zirconia particles and apolymerizable monomer.

Examples of the organic compounds having acidic groups include organiccompounds having at least one acidic group, such as a phosphoric acidgroup, a carboxylic acid group, a pyrophosphoric acid group, athiophosphoric acid group, a phosphonic acid group, and a sulfonic acidgroup. Preferred are phosphoric acid group-containing organic compoundshaving at least one phosphoric acid group, and carboxylic acidgroup-containing organic compounds having at least one carboxylic acidgroup, of which the phosphoric acid group-containing organic compoundsare more preferred. The zirconia particles may be subjected to a surfacetreatment with one type of surface treatment agent, or with two or moretypes of surface treatment agents. In the case where the zirconiaparticles are subjected to a surface treatment with two or more types ofsurface treatment agents, the surface treatment layer produced may be asurface treatment layer of a mixture of two or more surface treatmentagents, or a surface treatment layer of a multilayer structure of aplurality of surface treatment layers.

Examples of the phosphoric acid group-containing organic compoundsinclude 2-ethylhexyl acid phosphate, stearyl acid phosphate,2-(meth)acryloyloxyethyl dihydrogen phosphate, 3-(meth)acryloyloxypropyldihydrogen phosphate, 4-(meth)acryloyloxybutyl dihydrogen phosphate,5-(meth)acryloyloxypentyl dihydrogen phosphate, 6-(meth)acryloyloxyhexyldihydrogen phosphate, 7-(meth)acryloyloxyheptyl dihydrogen phosphate,8-(meth)acryloyloxyoctyl dihydrogen phosphate, 9-(meth)acryloyloxynonyldihydrogen phosphate, 10-(meth)acryloyloxydecyl dihydrogen phosphate,11-(meth)acryloyloxyundecyl dihydrogen phosphate,12-(meth)acryloyloxydodecyl dihydrogen phosphate,16-(meth)acryloyloxyhexadecyl dihydrogen phosphate,20-(meth)acryloyloxyicosyl dihydrogen phosphate,bis[2-(meth)acryloyloxyethyl]hydrogen phosphate,bis[4-(meth)acryloyloxybutyl]hydrogen phosphate,bis[6-(meth)acryloyloxyhexyl]hydrogen phosphate,bis[8-(meth)acryloyloxyoctyl]hydrogen phosphate,bis[9-(meth)acryloyloxynonyl]hydrogen phosphate,bis[10-(meth)acryloyloxydecyl]hydrogen phosphate,1,3-di(meth)acryloyloxypropyl dihydrogen phosphate,2-(meth)acryloyloxyethylphenyl hydrogen phosphate,2-(meth)acryloyloxyethyl-2-bromoethyl hydrogen phosphate,bis[2-(meth)acryloyloxy-(1-hydroxymethyl)ethyl]hydrogen phosphate, andacid chlorides, alkali metal salts, and ammonium salts thereof.

Examples of the carboxylic acid group-containing organic compoundsinclude succinic acid, oxalic acid, octanoic acid, decanoic acid,stearic acid, polyacrylic acid, 4-methyloctanoic acid, neodecanoic acid,pivalic acid, 2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid,2,2-dimethylvaleric acid, 2,2-diethylbutyric acid, 3,3-diethylbutyricacid, naphthenic acid, cyclohexane dicarboxylic acid, (meth)acrylicacid, N-(meth)acryloylglycine, N-(meth)acryloylaspartic acid,O-(meth)acryloyltyrosine, N-(meth)acryloyltyrosine,N-(meth)acryloyl-p-aminobenzoic acid, N-(meth)acryloyl-o-aminobenzoicacid, p-vinyl benzoic acid, 2-(meth)acryloyloxybenzoic acid,3-(meth)acryloyloxybenzoic acid, 4-(meth)acryloyloxybenzoic acid,N-(meth)acryloyl-5-aminosalicylic acid,N-(meth)acryloyl-4-aminosalicylic acid, 2-(meth)acryloyloxyethylhydrogen succinate, 2-(meth)acryloyloxyethyl hydrogen phthalate,2-(meth)acryloyloxyethyl hydrogen maleate,2-(2-(2-methoxyethoxy)ethoxy)acetic acid (commonly known as “MEEAA”),2-(2-methoxyethoxy)acetic acid (commonly known as “MEAA”), succinic acidmono[2-(2-methoxyethoxy)ethyl]ester, maleic acidmono[2-(2-methoxyethoxy)ethyl]ester, glutaric acidmono[2-(2-methoxyethoxy)ethyl]ester, malonic acid, glutaric acid,6-(meth)acryloyloxyhexane-1,1-dicarboxylic acid,9-(meth)acryloyloxynonane-1,1-dicarboxylic acid,10-(meth)acryloyloxydecane-1,1-dicarboxylic acid,11-(meth)acryloyloxyundecane-1,1-dicarboxylic acid,12-(meth)acryloyloxydodecane-1,1-dicarboxylic acid,13-(meth)acryloyloxytridecane-1,1-dicarboxylic acid,4-(meth)acryloyloxyethyl trimellitate, 4-(meth)acryloyloxybutyltrimellitate, 4-(meth)acryloyloxyhexyl trimellitate,4-(meth)acryloyloxydecyl trimellitate,2-(meth)acryloyloxyethyl-3′-(meth)acryloyloxy-2′-(3,4-dicarboxybenzoyloxy)propylsuccinate,and acid anhydrides, acid halides, alkali metal salts, and ammoniumsalts thereof.

It is also possible to use organic compounds having at least one acidicgroup different from the acidic groups mentioned above (e.g., apyrophosphoric acid group, a thiophosphoric acid group, a phosphonicacid group, and a sulfonic acid group).

For example, the organic compounds mentioned in WO2012/042911 may beused as such organic compounds.

Examples of the saturated fatty acid amides include palmitamide,stearamide, and behenamide. Examples of the unsaturated fatty acidamides include oleamide and erucamide. Examples of the saturated fattyacid bisamides include ethylene-bis-palmitamide,ethylene-bis-stearamide, and hexamethylene-bis-stearamide. Examples ofthe unsaturated fatty acid bisamides include ethylene-bis-oleamide,hexamethylene-bis-oleamide, and N,N′-dioleyl sebacamide.

Examples of the silane coupling agents (organosilicon compounds) includecompounds represented by R¹ _(n)SiX_(4-n) (wherein R¹ is a substitutedor unsubstituted hydrocarbon group of 1 to 12 carbon atoms, X is analkoxy group of 1 to 4 carbon atoms, a hydroxyl group, a halogen atom,or a hydrogen atom, and n is an integer of 0 to 3, and R¹ and X each maybe the same or different when a plurality of R¹ and X exists).

Specific examples of the silane coupling agents (organosiliconcompounds) include methyltrimethoxysilane, dimethyldimethoxysilane,phenyltrimethoxysilane, diphenyldimethoxysilane, methyltriethoxysilane,dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane,isobutyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane,vinyltris((-methoxyethoxy)silane, 3,3,3-trifluoropropyltrimethoxysilane,methyl-3,3,3-trifluoropropyldimethoxysilane,β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane,γ-methacryloyloxypropylmethyldimethoxysilane,γ-methacryloyloxypropylmethyldiethoxysilane, N-(β-aminoethyl)γ-aminopropylmethyldimethoxysilane, N-(β-aminoethyl)γ-aminopropyltrimethoxysilane, N-(β-aminoethyl)γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane,γ-mercaptopropyltrimethoxysilane, trimethylsilanol,methyltrichlorosilane, methyldichlorosilane, dimethyldichlorosilane,trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane,vinyltrichlorosilane, trimethylbromosilane, diethylsilane,vinyltriacetoxysilane, ω-(meth)acryloyloxyalkyltrimethoxysilane [3 to 12carbon atoms between the (meth)acryloyloxy group and the silicon atom,for example, such as in γ-methacryloyloxypropyltrimethoxysilane], andω-(meth)acryloyloxyalkyltriethoxysilane [3 to 12 carbon atoms betweenthe (meth)acryloyloxy group and the silicon atom, for example, such asin γ-methacryloyloxypropyltriethoxysilane]. As used herein, the notation“(meth)acryloyl” is meant to be inclusive of both methacryloyl andacryloyl.

Among these examples, silane coupling agents having functional groupsare preferred. Particularly preferred areω-(meth)acryloyloxyalkyltrimethoxysilane [3 to 12 carbon atoms betweenthe (meth)acryloyloxy group and the silicon atom],ω-(meth)acryloyloxyalkyltriethoxysilane [3 to 12 carbon atoms betweenthe (meth)acryloyloxy group and the silicon atom],vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, andγ-glycidoxypropyltrimethoxysilane.

Examples of the organic titanium compounds include tetramethyl titanate,tetraisopropyl titanate, tetra-n-butyl titanate, butyl titanate diners,and tetra(2-ethylhexyl)titanate.

Examples of the organic zirconium compounds include zirconiumisopropoxide, zirconium n-butoxide, zirconium acetylacetonate, zirconylacetate.

Examples of the organic aluminum compounds include aluminumacetylacetonate, and aluminum organic acid salt chelate compounds.

The surface treatment method is not particularly limited, and may be aknown method, for example, such as a method the adds the surfacetreatment agent by spraying it while vigorously stirring the zirconiaparticles, or a method that disperses or dissolves the zirconiaparticles and the surface treatment agent in a suitable solvent, andremoves the solvent. The solvent may be a dispersion medium containing aliquid having a surface tension at 25° C. of 50 mN/m or less, as will bedescribed later. The zirconia particles and the surface treatment agentmay be subjected to a reflux or a high-temperature high-pressure process(e.g., autoclaving) after being dispersed or dissolved.

According to the present invention, in producing a zirconia molded bodyusing the method having a molding step of molding zirconia particles,the molding step is not particularly limited. However, for advantagessuch as ease of production of the zirconia molded body of the presentinvention, and, in turn, the zirconia pre-sintered body and the zirconiasintered body of the present invention, the molding step is preferablyany one of the following steps:

-   (i) a step of slip casting a slurry containing zirconia particles;-   (ii) a step of gel casting a slurry containing zirconia particles;-   (iii) a step of pressing a powder containing zirconia particles;-   (iv) a step of molding a composition containing zirconia particles    and a resin; and-   (v) a step of polymerizing a composition containing zirconia    particles and a polymerizable monomer.

Zirconia Particle-Containing Slurry

A method for preparing a zirconia particle-containing slurry is notparticularly limited. For example, the zirconia particle-containingslurry may be one obtained after the breakdown or building-up processdescribed above, or may be a commercially available product.

When producing a zirconia molded body containing a colorant and/or atranslucency adjuster, and, in turn, a zirconia pre-sintered body and azirconia sintered body containing a colorant and/or a translucencyadjuster, the colorant and/or translucency adjuster may be added to theslurry containing zirconia particles and a fluorescent agent. In thiscase, it is preferable that the colorant and/or translucency adjuster bemixed into the zirconia particle-containing slurry in a liquid form suchas a solution or a dispersion.

Zirconia Particle-Containing Powder

The method of preparation of a zirconia particle-containing powder isnot particularly limited. However, for advantages such as obtaining amore homogenous zirconia sintered body of improved physical properties,it is preferable that the zirconia particle-containing powder beobtained by drying the zirconia particle-containing slurry. The slurrysubjected to drying may additionally contain a fluorescent agent and/ora colorant and/or a translucency adjuster.

The drying method is not particularly limited, and may be, for example,spray drying, supercritical drying, freeze drying, hot-air drying, anddrying under reduced pressure. For advantages such as inhibitingparticle aggregation during the drying process and obtaining a morecompact zirconia sintered body, it is preferable to use any of spraydrying, supercritical drying, and freeze drying, more preferably spraydrying or supercritical drying, even more preferably spray drying.

The zirconia particle-containing slurry to be dried may be a slurrycontaining water as dispersion medium. However, for advantages such asinhibiting particle aggregation during the drying process and obtaininga more compact zirconia sintered body, the slurry is preferably a slurrycontaining a dispersion medium other than water, for example, such as anorganic solvent.

Examples of the organic solvent include alcohols such as methanol,ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,2-methyl-2-propanol, 2-methoxyethanol, 2-ethoxyethanol,2-(2-ethoxyethoxy)ethanol, diethylene glycol monobutyl ether, andglycerin; ketones such as acetone, and methyl ethyl ketone; ethers suchas tetrahydrofuran, diethyl ether, diisopropyl ether, and 1,4-dioxane,and dimethoxyethane (including modified ethers such as propylene glycolmonomethyl ether acetate (commonly known as “PGMEA”), preferablyether-modified ethers and/or ester-modified ethers, more preferablyether-modified alkylene glycols and/or ester-modified alkylene glycols);esters such as ethyl acetate and butyl acetate; hydrocarbons such ashexane and toluene; and halogenated hydrocarbons such as chloroform andcarbon tetrachloride. These organic solvents may be used alone, or twoor more thereof may be used in combination. Considering safety againstthe body and ease of removal, the organic solvent is preferably awater-soluble organic solvent. Specifically, the organic solvent is morepreferably ethanol, 2-propanol, 2-methyl-2-propanol, 2-ethoxyethanol,2-(2-ethoxyethoxy)ethanol, propylene glycol monomethyl ether acetate,acetone, or tetrahydrofuran.

When using spray drying in particular, it is preferable that thedispersion medium in the zirconia particle- and fluorescentagent-containing slurry to be dried contain a liquid having a surfacetension at 25° C. of 50 mN/m or less because it enables a more compactzirconia sintered body to be obtained by inhibiting particle aggregationduring the drying process. From this viewpoint, the surface tension ofthe liquid is preferably 40 mN/m or less, more preferably 30 mN/m orless.

The surface tension at 25° C. may be a value from, for example, theHandbook of Chemistry and Physics. For liquids that are not included inthis reference, the values recited in WO2014/126034 are usable. Thesurface tensions at 25° C. of liquids that are not included in either ofthese documents may be determined by using a known measurement method,for example, such as the ring method or the Wilhelmy method. Preferably,the surface tension at 25° C. is measured using the automatic surfacetensiometer CBVP-Z manufactured by Kyowa Interface Science Co., Ltd., orthe SIGMA702 manufactured by KSV Instruments Ltd.

The liquid may be an organic solvent having the foregoing ranges ofsurface tension. The organic solvent may be any of the organic solventsexemplified above and having the foregoing ranges of surface tension.However, for advantages such as inhibiting particle aggregation duringthe drying process and obtaining a more compact zirconia sintered body,the organic solvent is preferably at least one selected from the groupconsisting of methanol, ethanol, 2-methoxyethanol, 1,4-dioxane,2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol, more preferably at leastone selected from the group consisting of methanol, ethanol,2-ethoxyethanol, and 2-(2-ethoxyethoxy)ethanol.

For advantages such as inhibiting particle aggregation during the dryingprocess and obtaining a more compact zirconia sintered body, the contentof the liquid in the dispersion medium is preferably 50 mass % or more,more preferably 80 mass % or more, even more preferably 95 mass % ormore, particularly preferably 99 mass % or more.

A slurry containing a dispersion medium other than water can be obtainedby replacing the dispersion medium in a slurry containing water asdispersion medium. The method used to replace the dispersion medium isnot particularly limited. For example, a method may be used that removeswater after adding a dispersion medium other than water (e.g., anorganic solvent) to a slurry containing water as dispersion medium. Inremoving water, part or all of the dispersion medium other than watermay be removed with water. The process of adding a dispersion mediumother than water and the subsequent removal of water may be repeatedmultiple times. Alternatively, a method may be used that precipitatesthe dispersoid after adding a dispersion medium other than water to aslurry containing water as dispersion medium. It is also possible toreplace the dispersion medium with a specific organic solvent in aslurry containing water as dispersion medium, followed by furtherreplacement with another organic solvent.

The fluorescent agent may be added after the replacement of dispersionmedium. However, for advantages such as obtaining a more homogenouszirconia sintered body of improved physical properties, the fluorescentagent is added preferably before the replacement of dispersion medium.Similarly, for advantages such as obtaining a more homogenous zirconiasintered body of improved physical properties, it is preferable to add acolorant and/or a translucency adjuster before the replacement ofdispersion medium when adding a colorant and/or a translucency adjusterto the slurry, though these may be added after the dispersion medium isreplaced.

The zirconia particle-containing slurry to be dried may be subjected toa dispersion process that involves heat and pressure, for example, suchas a reflux process or a hydrothermal treatment. The zirconiaparticle-containing slurry to be subjected to the drying step may besubjected to a mechanical dispersion process using, for example, aroller mill, a colloid mill, a high-pressure spray disperser, anultrasonic disperser, a vibration mill, a planetary mill, or a beadmill. The slurry may be subjected to only one of these processes, or twoor more of these processes.

The zirconia particle-containing slurry to be dried may additionallycontain one or more other components, for example, such as a binder, aplasticizer, a dispersant, an emulsifier, an antifoaming agent, a pHadjuster, and a lubricant. By containing such other components(particularly, for example, a binder, a dispersant, and an antifoamingagent), it may be possible to inhibit particle aggregation during thedrying process, and obtain a more compact zirconia sintered body.

Examples of the binder include polyvinyl alcohol, methylcellulose,carboxymethylcellulose, acrylic binders, wax binders, polyvinyl butyral,polymethylmethacrylate, and ethylcellulose.

Examples of the plasticizer include polyethylene glycol, glycerin,propylene glycol, and dibutyl phthalic acid.

Examples of the dispersant include ammonium polycarboxylates (e.g.,triammonium citrate), ammonium polyacrylates, acryl copolymer resins,acrylic acid ester copolymers, polyacrylic acids, bentonite,carboxymethylcellulose, anionic surfactants (for example,polyoxyethylene alkyl ether phosphate esters such as polyoxyethylenelauryl ether phosphate ester), non-ionic surfactants, oleic glycerides,amine salt surfactants, and oligosugar alcohols.

Examples of the emulsifier include alkyl ethers, phenyl ether, sorbitanderivatives, and ammonium salts.

Examples of the antifoaming agent include alcohols, polyethers,polyethylene glycol, silicone, and waxes.

Examples of the pH adjuster include ammonia, ammonium salts (includingammonium hydroxides such as tetramethylammonium hydroxide), alkali metalsalts, and alkali-earth metal salts.

Examples of the lubricant include polyoxyethylene alkylate ether, andwaxes.

For advantages such as inhibiting particle aggregation during the dryingprocess and obtaining a more compact zirconia sintered body, themoisture content in the zirconia particle-containing slurry to be driedis preferably 3 mass % or less, more preferably 1 mass % or less, evenmore preferably 0.1 mass % or less. The moisture content may be measuredwith a Karl Fisher moisture content meter.

The drying conditions in the foregoing drying methods are notparticularly limited, and may be appropriately selected from knowndrying conditions. When using an organic solvent as dispersion medium,it is preferable that drying be carried out in the presence of anonflammable gas, more preferably in the presence of nitrogen, in orderto reduce the risk of explosion during the drying process.

In the case of supercritical drying, the supercritical fluid is notparticularly limited, and may be, for example, water or carbon dioxide.However, for advantages such as inhibiting particle aggregation andobtaining a more compact zirconia sintered body, the supercritical fluidis preferably carbon dioxide.

Composition Containing Zirconia Particles and Resin

The method of preparation of a composition containing zirconia particlesand a resin is not particularly limited, and the composition may beobtained by, for example, mixing the zirconia particle-containing powderwith a resin.

Composition Containing Zirconia Particles and Polymerizable Monomer

The method of preparation of a composition containing zirconia particlesand a polymerizable monomer is not particularly limited, and thecomposition may be obtained by, for example, mixing the zirconiaparticle-containing powder with a polymerizable monomer.

(i) Slip Casting

In producing a zirconia molded body by the method that includes a stepof slip casting a zirconia particle-containing slurry, the slip castingmethod is not particularly limited, and may be, for example, a method inwhich a zirconia particle-containing slurry is dried after being pouredinto a mold.

For advantages such as ease of pouring into a mold, and increasing theusable lifetime of a mold by preventing long drying times, the contentof the dispersion medium in the zirconia particle-containing slurry usedis preferably 80 mass % or less, more preferably 50 mass % or less, evenmore preferably 20 mass % or less.

The slurry may be poured into a mold under ordinary pressure. However,it is preferable for production efficiency that the slurry be pouredinto a mold under increased pressure conditions. The type of the moldused for slip casting is not particularly limited, and the mold may be,for example, a porous mold made of plaster, resin, ceramic, or the like.Resin molds and ceramic molds are desirable in terms of durability.

The zirconia particle-containing slurry used for slip casting mayadditionally contain one or more other components such as above, forexample, such as a binder, a plasticizer, a dispersant, an emulsifier,an antifoaming agent, a pH adjuster, and a lubricant.

(ii) Gel Casting

In producing a zirconia molded body by the method that includes a stepof gel casting a zirconia particle-containing slurry, the gel castingmethod is not particularly limited, and may be, for example, a method inwhich a zirconia particle- and fluorescent agent-containing slurry isshaped into a wet body by a process such as gelation, followed bydrying.

For advantages such as preventing long drying times and inhibitingcracking during drying, the content of the dispersion medium in thezirconia particle-containing slurry used is preferably 80 mass % orless, more preferably 50 mass % or less, even more preferably 20 mass %or less.

The gelation may be initiated by addition of, for example, agelatinizer, or may be achieved by adding and polymerizing apolymerizable monomer. The type of the mold used is not particularlylimited, and the mold may be, for example, a porous mold made ofplaster, resin, ceramic, or the like, or a nonporous mold made of metal,resin, or the like.

The type of gelatinizer is not particularly limited, and, for example, awater-soluble gelatinizer may be used. Specifically, for example,agarose or gelatin may preferably be used. The gelatinizer may be onekind of gelatinizer used alone, or may be two or more kinds ofgelatinizers used in combination. For considerations such as inhibitingcracking during sintering, the gelatinizer content is preferably 10 mass% or less, more preferably 5 mass % or less, even more preferably 1 mass% or less relative to the mass of the slurry after the gelatinizer isadded.

The type of polymerizable monomer is not particularly limited. Examplesof the polymerizable monomer include 2-hydroxyethyl(meth)acrylate,3-hydroxypropyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,6-hydroxyhexyl(meth)acrylate, 10-hydroxydecyl(meth)acrylate, propyleneglycol mono(meth)acrylate, glycerol mono(meth)acrylate, erythritolmono(meth)acrylate, N-methylol(meth)acrylamide,N-hydroxyethyl(meth)acrylamide, andN,N-bis(2-hydroxyethyl)(meth)acrylamide. The polymerizable monomer maybe used alone, or two or more thereof may be used in combination.

For considerations such as inhibiting cracking during sintering, thecontent of the polymerizable monomer is preferably 10 mass % or less,more preferably 5 mass % or less, even more preferably 1 mass % or lessrelative to the mass of the slurry after the polymerizable monomer isadded.

When gelation is achieved by polymerization of the polymerizablemonomer, the polymerization is carried out preferably with use of apolymerization initiator. The type of polymerization initiator is notparticularly limited. However, the polymerization initiator isparticularly preferably a photopolymerization initiator. Thephotopolymerization initiator may be appropriately selected fromphotopolymerization initiators commonly used in industry, preferablyfrom photopolymerization initiators used in dentistry.

Specific examples of the photopolymerization initiator include(bis)acylphosphine oxides (including salts), thioxanthones (includingsalts such as quaternary ammonium salts), ketals, α-diketones,coumarins, anthraquinones, benzoinalkyl ether compounds, andα-aminoketone compounds. The photopolymerization initiator may be usedalone, or two or more thereof may be used in combination. Among these,the photopolymerization initiator is preferably at least one selectedfrom the group consisting of (bis)acylphosphine oxides and α-diketones.In this way, polymerization (gelation) can be achieved both in theultraviolet region (including the near-ultraviolet region) and in thevisible light region. Specifically, polymerization (gelation) cansufficiently proceed regardless of whether the light source is a lasersuch as an Ar laser or a He—Cd laser; or a light such as a halogen lamp,a xenon lamp, a metal halide lamp, a light emitting diode (LED), amercury lamp, and a fluorescent lamp.

Examples of the acylphosphine oxides in the (bis)acylphosphine oxidesinclude 2,4,6-trimethylbenzoyldiphenylphosphine oxide (commonly known as“TPO”), 2,6-dimethoxybenzoyldiphenylphosphine oxide,2,6-dichlorobenzoyldiphenylphosphine oxide,2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide,2,4,6-trimethylbenzoylethoxyphenylphosphine oxide,2,3,5,6-tetramethylbenzoyldiphenylphosphine oxide, benzoyldi(2,6-dimethylphenyl)phosphonate, sodium salts of2,4,6-trimethylbenzoylphenylphosphine oxide, potassium salts of2,4,6-trimethylbenzoylphenylphosphine oxide, and ammonium salts of2,4,6-trimethylbenzoylphenylphosphine oxide.

Examples of the bisacylphosphine oxides in the (bis)acylphosphine oxidesinclude bis(2,6-dichlorobenzoyl)phenylphosphine oxide,bis(2,6-dichlorobenzoyl)-2,5-dimethylphenylphosphine oxide,bis(2,6-dichlorobenzoyl)-4-propylphenylphosphine oxide,bis(2,6-dichlorobenzoyl)-1-naphthylphosphine oxide,bis(2,6-dimethoxybenzoyl)phenylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide,bis(2,6-dimethoxybenzoyl)-2,5-dimethylphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, andbis(2,3,6-trimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide. It isalso possible to use other compounds, including, for example, thecompounds mentioned in JP-A-2000-159621.

Preferred among these (bis)acylphosphine oxides are2,4,6-trimethylbenzoyldiphenylphosphine oxide,2,4,6-trimethylbenzoylmethoxyphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, and sodium salts of2,4,6-trimethylbenzoylphenylphosphine oxide.

Examples of the α-diketones include diacetyl, benzyl, camphorquinone,2,3-pentadione, 2,3-octadione, 9,10-phenanthrenequinone, 4,4′-oxybenzyl,and acenaphthenequinone. Preferred is camphorquinone, particularly whenusing a light source of the visible light region.

The zirconia particle-containing slurry used for gel casting mayadditionally contain one or more other components such as, for example,such as a binder, a plasticizer, a dispersant, an emulsifier, anantifoaming agent, a pH adjuster, and a lubricant, as with the case ofthe slurry used for slip casting.

The method of drying the shaped wet body is not particularly limited,and may be, for example, natural drying, hot-air drying, vacuum drying,dielectric heating, induction heating, or constant-temperatureconstant-humidity drying. The drying may be achieved by using one ofthese methods, or two or more of these methods. For advantages such asinhibiting cracking during drying, the preferred drying methods arenatural drying, dielectric heating, induction heating, andconstant-temperature constant-humidity drying.

(iii) Pressing

In producing a zirconia molded body by the method that includes a stepof pressing a powder containing zirconia particles, the pressing is notparticularly limited to specific methods, and may be achieved by using aknown pressing machine. Specific examples of the pressing method includeuniaxial pressing. In order to increase the density of the zirconiamolded body produced, it is preferable that uniaxial pressing befollowed by cold isostatic pressing (CIP).

The zirconia particle-containing powder used for pressing mayadditionally contain one or more other components such as above, forexample, such as a binder, a plasticizer, a dispersant, an emulsifier,an antifoaming agent, a pH adjuster, and a lubricant. These componentsmay be added at the time of preparing the powder.

(iv) Molding of Resin-Containing Composition

In producing a zirconia molded body by the method that includes a stepof molding a composition containing zirconia particles and a resin, thecomposition molding method is not limited to specific methods, and thecomposition may be molded by using a method, for example, such asinjection molding, cast molding, and extrusion molding. It is alsopossible to shape the composition using a lamination shaping technique(e.g., 3D printing), for example, such as fused deposition modeling(FDM), an inkjet method, or a powder-binder lamination technique.Preferred as the molding method are injection molding and cast molding,more preferably injection molding.

The resin is not limited to particular types of resins, and resins thatfunction as binders may preferably be used. Specific examples of theresin include fatty acids such as paraffin wax, polyvinyl alcohol,polyethylene, a polypropylene, ethylene-vinyl acetate copolymer,polystyrene, atactic polypropylene, methacrylate resin, and stearicacid. These resins may be used alone, or two or more thereof may be usedin combination.

The composition containing zirconia particles and a resin mayadditionally contain one or more other components such as above, forexample, such as a binder, a plasticizer, a dispersant, an emulsifier,an antifoaming agent, a pH adjuster, and a lubricant.

(v) Polymerization of Composition Containing Polymerizable Monomer

Polymerization of the composition containing zirconia particles and apolymerizable monomer can polymerize the polymerizable monomer in thecomposition, and cure the composition. In producing a zirconia moldedbody by the method that includes a polymerization step, the method isnot particularly limited to specific methods, and may be, for example,(a) a method that polymerizes the zirconia particle- and polymerizablemonomer-containing composition in a mold; or (b) stereolithography (SLA)using the composition containing zirconia particles and a polymerizablemonomer. Of these, (b) stereolithography is preferred. Bystereolithography, a shape corresponding to the shape desired for theproduct zirconia sintered body can be imparted to the zirconia moldedbody at the time of its production. This makes the stereolithography apotentially preferred method, particularly when the zirconia sinteredbody of the present invention is used as a dental material such as adental prosthesis.

The type of the polymerizable monomer in the zirconia particle- andpolymerizable monomer-containing composition is not particularlylimited, and the polymerizable monomer may be one selected frommonofunctional polymerizable monomers such as monofunctional(meth)acrylates, and monofunctional (meth)acrylamides, andpolyfunctional polymerizable monomers such as bifunctional aromaticcompounds, bifunctional aliphatic compounds, and tri and higherfunctional compounds. The polymerizable monomer may be used alone, ortwo or more thereof may be used. Among these, polyfunctionalpolymerizable monomers are preferred, particularly whenstereolithography is used.

Examples of the monofunctional (meth)acrylates include (meth)acrylateshaving hydroxyl groups, such as 2-hydroxyethyl(meth)acrylate,2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, 6-hydroxyhexyl(meth)acrylate,10-hydroxydecyl(meth)acrylate, propylene glycol mono(meth)acrylate,glycerol mono(meth)acrylate, and erythritol mono(meth)acrylate;alkyl(meth)acrylates such as methyl(meth)acrylate, ethyl(meth)acrylate,propyl(meth)acrylate, isopropyl(meth)acrylate, n-butyl(meth)acrylate,sec-butyl(meth)acrylate, t-butyl(meth)acrylate, isobutyl(meth)acrylate,n-hexyl(meth)acrylate, lauryl(meth)acrylate, cetyl(meth)acrylate, andstearyl(meth)acrylate; alicyclic(meth)acrylates, such ascyclohexyl(meth)acrylate, and isobornyl(meth)acrylate; aromaticgroup-containing(meth)acrylates, such as benzyl(meth)acrylate, andphenyl(meth)acrylate; and (meth)acrylates having functional groups, suchas 2,3-dibromopropyl(meth)acrylate,3-(meth)acryloyloxypropyltrimethoxysilane, and11-(meth)acryloyloxyundecyltrimethoxysilane.

Examples of the monofunctional (meth)acrylamides include(meth)acrylamide, N-(meth)acryloylmorpholine,N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide,N,N-di-n-propyl(meth)acrylamide, N,N-di-n-butyl(meth)acrylamide,N,N-di-n-hexyl(meth)acrylamide, N,N-di-n-octyl(meth)acrylamide,N,N-di-2-ethylhexyl(meth)acrylamide, N-hydroxyethyl(meth)acrylamide, andN,N-di(hydroxyethyl)(meth)acrylamide.

Among these monofunctional polymerizable monomers, (meth)acrylamides arepreferred, and N-(meth)acryloylmorpholine, N,N-dimethyl(meth)acrylamide,and N,N-diethyl(meth)acrylamide are more preferred for their desirablepolymerizability.

Examples of the bifunctional aromatic compounds include2,2-bis((meth)acryloyloxyphenyl)propane,2,2-bis[4-(3-(meth)acryloyloxy-2-hydroxypropoxy)phenyl]propane,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane (commonlyknown as “Bis-GMA”), 2,2-bis(4-(meth)acryloyloxyethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxydiethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxytetraethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxypentaethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxydipropoxyphenyl)propane,2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxyethoxyphenyl)propane,2-(4-(meth)acryloyloxydiethoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane,2-(4-(meth)acryloyloxydipropoxyphenyl)-2-(4-(meth)acryloyloxytriethoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxypropoxyphenyl)propane,2,2-bis(4-(meth)acryloyloxyisopropoxyphenyl)propane, and1,4-bis(2-(meth)acryloyloxyethyl)pyromellitate. Among these,2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane (commonlyknown as “Bis-GMA”), and2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane are preferred fortheir desirable polymerizability and ability to provide desirablestrength for the zirconia molded body produced. Preferred as2,2-bis(4-(meth)acryloyloxypolyethoxyphenyl)propane is2,2-bis(4-methacryloyloxypolyethoxyphenyl)propane (a compound with anaverage number of moles of ethoxy group added of 2.6; commonly known as“D-2.6E”).

Examples of the bifunctional aliphatic compounds include glyceroldi(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycoldi(meth)acrylate, triethylene glycol di(meth)acrylate, propylene glycoldi(meth)acrylate, butylene glycol di(meth)acrylate, neopentyl glycoldi(meth)acrylate, polyethylene glycol di(meth)acrylate, 1,3-butanedioldi(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, 2-ethyl-1,6-hexanediol di(meth)acrylate,1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate,1,2-bis(3-methacryloyloxy-2-hydroxypropoxy)ethane, and2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl)dimethacrylate(commonly known as “UDMA”). Among these, triethylene glycoldimethacrylate (commonly known as “TEGDMA”), and2,2,4-trimethylhexamethylene bis(2-carbamoyloxyethyl)dimethacrylate arepreferred for their desirable polymerizability and ability to providedesirable strength for the zirconia molded body produced.

Examples of the tri and higher functional compounds includetrimethylolpropane tri(meth)acrylate, trimethylolethanetri(meth)acrylate, trimethylolmethane tri(meth)acrylate, pentaerythritoltri(meth)acrylate, pentaerythritol tetra(meth)acrylate,dipentaerythritol penta(meth)acrylate,N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetra(meth)acrylate,and 1,7-diacryloyloxy-2,2,6,6-tetra(meth)acryloyloxymethyl-4-oxyheptane.Among these,N,N-(2,2,4-trimethylhexamethylene)bis[2-(aminocarboxy)propane-1,3-diol]tetramethacrylate,and 1,7-diacryloyloxy-2,2,6,6-tetraacryloyloxymethyl-4-oxyheptane arepreferred for their desirable polymerizability and ability to providedesirable strength for the zirconia molded body produced.

Regardless of whether the method (a) or (b) is used, it is preferablethat a polymerization initiator be used for the polymerization of thecomposition, and that the composition contain a polymerizationinitiator. The type of polymerization initiator is not particularlylimited, and the polymerization initiator is particularly preferably aphotopolymerization initiator. The photopolymerization initiator may beappropriately selected from photopolymerization initiators commonly usedin industry, preferably from photopolymerization initiators used indentistry. Specific examples of the photopolymerization initiatorinclude those exemplified above in conjunction with gel casting, and areomitted to avoid redundancy.

The composition containing zirconia particles and a polymerizablemonomer may additionally contain one or more other components such asabove, for example, such as a binder, a plasticizer, a dispersant, anemulsifier, an antifoaming agent, a pH adjuster, and a lubricant.

In producing a zirconia molded body by stereolithography using thecomposition containing zirconia particles and a polymerizable monomer,the stereolithography is not particularly limited to specific methods,and may be achieved by appropriately using a known method. For example,the desired zirconia molded body may be obtained by forming layers ofdesired shapes layer-by-layer through photo-polymerization of a liquidcomposition with, for example, ultraviolet light or a laser, using astereolithography device.

In obtaining the zirconia molded body by stereolithography, the contentof the zirconia particles in the zirconia particle- and polymerizablemonomer-containing composition should preferably be as high as possiblefrom the viewpoint of sinterability in a later step. Specifically, thezirconia particle content is preferably 20 mass % or more, morepreferably 30 mass % or more, even more preferably 40 mass % or more,particularly preferably 50 mass % or more. From the principle of layerformation in stereolithography, it is preferable that the compositionhave a viscosity that falls in a certain range. To this end, the contentof the zirconia particles in the composition is preferably 90 mass % orless, more preferably 80 mass % or less, even more preferably 70 mass %or less, particularly preferably 60 mass % or less. Adjustment ofcomposition viscosity may be of particular importance whenstereolithography is performed using the constrained surface method, inwhich light is applied upward through the bottom of a container to forma zirconia molded body layer-by-layer, and when the composition needs tobe smoothly flown in between the bottom surface of the previously curedlayer and the bottom of the container for the formation of the nextlayer after the cured layer is elevated upward by the height of onelayer.

Specifically, the composition has a viscosity of preferably 20,000 mPa·sor less, more preferably 10,000 mPa·s or less, even more preferably5,000 mPa·s or less, and is preferably 100 mPa·s or more, in terms of aviscosity at 25° C. Because the viscosity of the composition tends toincrease with increase of the zirconia particle content, it ispreferable to appropriately adjust the balance between zirconia particlecontent and viscosity in the composition in a way suited for theperformance and other characteristics of the stereolithography device,taking into consideration factors such as the balance between the rateof the stereolithography process and the accuracy of the zirconia moldedbody produced. The viscosity may be measured with an E-type viscometer.

In the method of production of the zirconia molded body of the presentinvention, a zirconia molded body may be subjected to CIP after beingsubjected to humidification treatment, to further improve the density ofthe zirconia molded body. In the case where pressing is carried out, azirconia particle-containing powder may be pressed after being subjectedto humidification treatment. Any known humidification treatment may beused with no limitation. Humidification treatment may be carried out byspraying water with a spray or the like, or by using a hygrostat,thermo-hygrostat, or the like. A moisture content increased by thehumidification treatment depends for example on the particle diameter ofcontained zirconia particles. However, the increased moisture contentrelative to the mass of powder and a molded body before getting wet ispreferably more than 2 mass %, more preferably more than 3 mass %, evenmore preferably more than 4 mass %, particularly preferably more than 5mass %, and is preferably 15 mass % or less, more preferably 13 mass %or less, even more preferably 11 mass % or less. Note that the moisturecontent increased by humidification treatment may be determined as avalue in percentage by dividing a value resulting from subtraction ofthe mass of the powder and the molded body before getting wet from themass of the powder and the molded body after getting wet, by the mass ofthe powder and the molded body before getting wet.

Zirconia Pre-Sintered Body

The zirconia pre-sintered body of the present invention is characterizedby containing 2.0 to 9.0 mol % yttria and having ΔL*(W−B) of 5 or morethrough a thickness of 1.5 mm. With use of the zirconia pre-sinteredbody, it is possible to obtain a zirconia sintered body that excels inboth translucency and strength and excels in linear light transmittance.

When producing a zirconia sintered body of the present inventioncontaining a fluorescent agent, it is preferable that the fluorescentagent be contained in the zirconia pre-sintered body. The content of thefluorescent agent in the zirconia pre-sintered body of the presentinvention may be appropriately adjusted according to, for example, thecontent of the fluorescent agent in the zirconia sintered body to beproduced. Specifically, the content of the fluorescent agent containedin the zirconia pre-sintered body is preferably 0.001 mass % or more,more preferably 0.005 mass % or more, even more preferably 0.01 mass %or more, and is preferably 1 mass % or less, more preferably 0.5 mass %or less, even more preferably 0.1 mass % or less in terms of an oxide ofthe metallic element contained in the fluorescent agent, relative to themass of the zirconia contained in the zirconia pre-sintered body.

When producing a zirconia sintered body containing a colorant, it ispreferable that the colorant be contained in the zirconia pre-sinteredbody. The content of the colorant in the zirconia pre-sintered body ofthe present invention may be appropriately adjusted according to, forexample, the content of the colorant in the zirconia sintered body to beproduced. Specifically, the content of the colorant in the zirconiapre-sintered body is preferably 0.001 mass % or more, more preferably0.005 mass % or more, even more preferably 0.01 mass % or more, and ispreferably 5 mass % or less, more preferably 1 mass % or less, even morepreferably 0.5 mass % or less, and may be 0.1 mass % or less, or 0.05mass % or less in terms of an oxide of the metallic element contained inthe colorant, relative to the mass of the zirconia contained in thezirconia pre-sintered body.

When producing a zirconia sintered body containing a translucencyadjuster, it is preferable that the translucency adjuster be containedin the zirconia pre-sintered body. The content of the translucencyadjuster in the zirconia pre-sintered body of the present invention maybe appropriately adjusted according to, for example, the content of thetranslucency adjuster in the zirconia sintered body to be produced.Specifically, the content of the translucency adjuster contained in thezirconia pre-sintered body is preferably 0.1 mass % or less relative tothe mass of the zirconia contained in the zirconia pre-sintered body.

The yttria content in the zirconia pre-sintered body of the presentinvention may be the same as that in the zirconia sintered body to beproduced, within a range of 2.0 to 9.0 mol %. Specifically, the yttriacontent in the zirconia pre-sintered body is 2.0 mol % or more,preferably 3.0 mol % or more, more preferably 4.0 mol % or more, and is9.0 mol % or less, preferably 8.0 mol % or less, more preferably 7.0 mol% or less. It is to be noted that the yttria content in the zirconiapre-sintered body is a fraction (mol %) of the number of moles of yttriawith respect to the total number of moles of zirconia and yttria.

The density of the zirconia pre-sintered body of the present inventionis not particularly limited, and preferably falls in a range of 3.0 to6.0 g/m³, more preferably 3.2 to 5.8 g/m³, though the density varieswith conditions such as the method of production of the zirconia moldedbody used for the production of the zirconia pre-sintered body.

The shape of the zirconia pre-sintered body of the present invention isnot particularly limited, and may be chosen as desired according to use.However, for example, considering ease of handing of when using thezirconia pre-sintered body as a mill blank for producing a dentalmaterial such as a dental prosthesis, the zirconia pre-sintered bodypreferably has a disc or a prism shape (e.g., rectangular). The zirconiapre-sintered body may be cut (milled) into the desired shape accordingto use before being formed into a zirconia sintered body, as will bedescribed later. However, the present invention also encompasseszirconia pre-sintered bodies of desired shapes imparted after cutting(milling). The zirconia pre-sintered body may have a monolayer structureor a multilayer structure. However, with a multilayered zirconiapre-sintered body, the resulting zirconia sintered body can have amultilayer structure, which allows translucency and other physicalproperties to be locally altered.

For advantages such as maintaining the shape of the work in the processof working using a cutting machine, and improving the ease of cuttingitself, the three-point flexural strength of the zirconia pre-sinteredbody of the present invention preferably falls in a range of 10 to 70MPa, more preferably 20 to 60 MPa. The three-point flexural strength ofthe zirconia pre-sintered body may be a measured value obtained from a 5mm×40 mm×10 mm specimen using a multi-purpose tester at a span length of30 mm and a crosshead speed of 0.5 mm/min.

The zirconia pre-sintered body of the present invention has a crystalgrain size of preferably 180 nm or less after being sintered at 900 to1,200° C. for 2 hours under ordinary pressure (after being formed into azirconia sintered body). In this way, the zirconia sintered body of thepresent invention having excellent translucency can be produced withease. For advantages such as obtaining a zirconia sintered body havingeven higher translucency, the crystal grain size is more preferably 140nm or less, even more preferably 120 nm or less, further even morepreferably 115 nm or less, and may be 110 nm or less. The lower limit ofcrystal grain size is not particularly limited, and the crystal grainsize may be, for example, 50 nm or more, or 100 nm or more. The crystalgrain size can be measured in the same manner as in the crystal grainsize measurement described above in conjunction with the zirconiasintered body.

The zirconia pre-sintered body of the present invention has ΔL*(W−B) of5 or more, preferably 7 or more, more preferably 10 or more, through athickness of 1.5 mm. With the ΔL*(W−B) in the range as above, a zirconiasintered body having high linear light transmittance can be obtainedafter being sintered under ordinary pressure. The upper limit ofΔL*(W−B) is not particularly limited, and may be, for example, 30 orless, or 25 or less. The ΔL*(W−B) of zirconia pre-sintered body througha thickness of 1.5 mm may be measured with a spectrophotometer. Forexample, a spectrophotometer (CM-3610A manufactured by Konica MinoltaJapan) may be used for the measurement. In the measurement, the ΔL*(W−B)may be determined by using F11 as a light source and measuring reflectedlight. The specimen used for measurement may be a disc-shaped zirconiapre-sintered body measuring 20 mm in diameter and 1.5 mm in thickness.

The zirconia pre-sintered body of the present invention has athree-point flexural strength of preferably 500 MPa or more after beingsintered at 900 to 1,200° C. under ordinary pressure (after being formedinto a zirconia sintered body). In this way, the zirconia sintered bodyof the present invention having excellent strength can be produced withease. For advantages such as obtaining a zirconia sintered body havingeven higher strength, the three-point flexural strength is morepreferably 600 MPa or more, even more preferably 650 MPa or more,further even more preferably 700 MPa or more, particularly preferably800 MPa or more. The upper limit of three-point flexural strength is notparticularly limited, and the three-point flexural strength may be, forexample, 1,500 MPa or less, or 1,000 MPa or less. The three-pointflexural strength can be measured in the same manner as in themeasurement of three-point flexural strength described above inconjunction with the zirconia sintered body.

The zirconia pre-sintered body of the present invention has atransmittance of preferably 40% or more for light of 700 nm wavelengththrough a thickness of 0.5 mm after being sintered at 900 to 1,200° C.under ordinary pressure (after being formed into a zirconia sinteredbody). In this way, the zirconia sintered body of the present inventionhaving excellent translucency can be produced with ease. For advantagessuch as obtaining a zirconia sintered body having even highertranslucency, the transmittance is more preferably 45% or more, evenmore preferably 46% or more, further even more preferably 48% or more,particularly preferably 50% or more, and may be 52% or more. The upperlimit of transmittance is not particularly limited, and thetransmittance may be, for example, 60% or less, or 57% or less. Thetransmittance can be measured in the same manner as in the measurementof transmittance for light of 700 nm wavelength through a thickness of0.5 mm described above in conjunction with the zirconia sintered body.

The zirconia pre-sintered body of the present invention has a linearlight transmittance of preferably 1% or more, more preferably 3% ormore, even more preferably 5% or more, further even more preferably 7%or more, and may be 10% or more, through a thickness of 1.0 mm afterbeing sintered at 900 to 1,200° C. under ordinary pressure (after beingformed into a zirconia sintered body). With the linear lighttransmittance falling in these ranges, the zirconia sintered body canmore easily satisfy the level of translucency required for the incisalregion when used as, for example, a dental prosthesis. The upper limitof linear light transmittance is not particularly limited, and thelinear light transmittance may be, for example, 60% or less, or 50% orless. The linear light transmittance can be measured in the same manneras in the measurement of linear light transmittance through a thicknessof 1.0 mm described above in conjunction with the zirconia sinteredbody.

Method of Production of Zirconia Pre-Sintered Body

The method of production of the zirconia pre-sintered body of thepresent invention is, for example, characterized by using the zirconiamolded body of the present invention, and preferably includes a step ofpre-sintering the zirconia molded body at 200 to 800° C. For advantagessuch as ease of obtaining the desired zirconia pre-sintered body, thepre-sintering temperature is preferably 200° C. or more, more preferably250° C. or more, even more preferably 300° C. or more, and is preferably800° C. or less, more preferably 700° C. or less, even more preferably600° C. or less. With a pre-sintering temperature equal to or greaterthan the foregoing lower limits, it is possible to effectively inhibitgeneration of organic material residues. With a pre-sinteringtemperature equal to or less than the foregoing upper limits, it ispossible to reduce the difficulty in cutting (milling) with a cuttingmachine occurring when the sintering overly proceeds.

The rate of temperature increase in pre-sintering of the zirconia moldedbody of the present invention is not particularly limited, and ispreferably 0.1° C./min or more, more preferably 0.2° C./min or more,even more preferably 0.5° C./min or more, and is preferably 50° C./minor less, more preferably 30° C./min or less, even more preferably 20°C./min or less. The productivity improves when the rate of temperatureincrease is equal to or greater than the foregoing lower limits. With arate of temperature increase equal to or less than the foregoing upperlimits, it is possible to reduce the volume difference between inner andouter portions of the zirconia molded body and the zirconia pre-sinteredbody, and to reduce cracking and breakage by inhibiting the organicmaterials from undergoing rapid decomposition when the zirconia moldedbody is containing organic materials.

The pre-sintering time in the pre-sintering of the zirconia molded bodyof the present invention is not particularly limited. However, foradvantages such as efficiently and stably obtaining the desired zirconiapre-sintered body with good productivity, the pre-sintering time ispreferably 0.5 hours or more, more preferably 1 hour or more, even morepreferably 2 hours or more, and is preferably 10 hours or less, morepreferably 8 hours or less, even more preferably 6 hours or less.

Pre-sintering in the present invention may be carried out using apre-sintering furnace. The type of pre-sintering furnace is notparticularly limited, and the pre-sintering furnace may be, for example,an electric furnace or a debinding furnace commonly used in industry.

The zirconia pre-sintered body of the present invention may be cut(milled) into the desired shape according to use, before being formedinto a zirconia sintered body. To describe more specifically, thezirconia sintered body of the present invention excels in bothtranslucency and strength despite containing a fluorescent agent, and isparticularly preferred as, for example, a dental material such as adental prosthesis. To this end, the zirconia pre-sintered body may becut (milled) into a shape corresponding to the shape of such a materialso that a zirconia sintered body for use in such applications can beobtained. Cutting (milling) is not limited to specific methods, and maybe achieved by using, for example, a known milling device.

Method of Production of Zirconia Sintered Body

As described above, the zirconia sintered body of the present inventioncan be produced by sintering the zirconia molded body of the presentinvention under ordinary pressure, and also can be produced by sinteringthe zirconia pre-sintered body of the present invention under ordinarypressure.

For advantages such as ease of obtaining the desired zirconia sinteredbody, the sintering temperature is preferably 900° C. or more, morepreferably 1,000° C. or more, even more preferably 1,050° C. or more,and also for advantages such as ease of obtaining the desired zirconiasintered body, the sintering temperature is preferably 1,200° C. orless, more preferably 1,150° C. or less, even more preferably 1,120° C.or less, regardless of whether the zirconia molded body of the presentinvention or the zirconia pre-sintered body of the present invention issintered. With a sintering temperature equal to or greater than theforegoing lower limits, sintering can sufficiently proceed, and acompact sintered body can be obtained with ease. With a sinteringtemperature equal to or less than the foregoing upper limits, it ispossible to easily obtain a zirconia sintered body having a crystalgrain size within the preferable ranges of the present invention, and toinhibit deactivation of fluorescent agent.

In sintering the zirconia molded body of the present invention and thezirconia pre-sintered body of the present invention, the sintering timeis not particularly limited; however, for advantages such as efficientlyand stably obtaining the desired zirconia sintered body with goodproductivity, the sintering time is preferably 5 minutes or more, morepreferably 15 minutes or more, even more preferably 30 minutes or more,and is preferably 6 hours or less, more preferably 4 hours or less, evenmore preferably 2 hours or less, regardless of whether the zirconiamolded body of the present invention or the zirconia pre-sintered bodyof the present invention is sintered.

Sintering in the present invention may be carried out using a sinteringfurnace. The type of sintering furnace is not particularly limited, andthe sintering furnace may be, for example, an electric furnace or adebinding furnace commonly used in industry. Specifically, when thezirconia sintered body is to be used for dental material applications,it is possible to use a dental porcelain furnace, which operates in arelatively low sintering temperature range, other than using atraditional dental sintering furnace for zirconia.

The zirconia sintered body of the present invention can be produced withease without HIP. However, further improvement of translucency andstrength can be achieved when the sintering under ordinary pressure isfollowed by HIP.

Use of Zirconia Sintered Body

The zirconia sintered body of the present invention is not limited toparticular applications. However, because the zirconia sintered body ofthe present invention excels in both translucency and strength andexcels in linear light transmittance, the zirconia sintered body of thepresent invention is particularly preferred as a dental material such asa dental prosthesis, and is highly useful not only as a dentalprosthesis for the cervical region of a tooth, but as a dentalprosthesis for the occlusal surface of a posterior tooth, and theincisal region of a front tooth. The zirconia sintered body of thepresent invention is particularly preferred for use as a dentalprosthesis for the incisal region of a front tooth.

EXAMPLES

The following describes the present invention in greater detail usingExamples and Comparative Examples. It is to be noted, however, that thepresent invention is not limited by the following descriptions. Themethods used to measure physical properties are as follows.

(1) Average Primary Particle Diameter of Zirconia Particles

The average primary particle diameter of zirconia particles wasdetermined by taking a micrograph of zirconia particles with atransmission electron microscope (TEM), and finding a mean value ofparticle diameters (maximum diameters) measured for arbitrarily chosen100 particles from the photographed image.

(2) Fraction of Particles Having Particle Diameter of More than 100 nm

Zirconia particles were dispersed in methanol and measurement wasperformed with a laser diffraction/scattering particle size distributionanalyzer (LA-950 manufactured by Horiba Ltd.).

(3) Crystal Grain Size

The crystal grain size of zirconia sintered body was determined bytaking a micrograph of zirconia sintered body cross sections with afield emission scanning electron microscope (FE-SEM), and finding a meanvalue of diameters of circles corresponding to 10 arbitrarily selectedparticles from the micrograph (the diameters of true circles having thesame areas as these particles).

(4) Three-Point Flexural Strength

The three-point flexural strength of zirconia sintered body was measuredin compliance with ISO 6872:2015. A specimen measuring 4 mm×1.2 mm×15 mmin size was produced from a plate-shaped zirconia sintered body of eachof Examples and Comparative Examples, and the measurement was performedon the specimen with a multi-purpose tester at a span length of 12 mmand a crosshead speed of 0.5 mm/min.

(5) Light Transmittance (700 nm Wavelength, 0.5 mm Thickness)

The transmittance of zirconia sintered body for light of 700 nmwavelength through a thickness of 0.5 mm was measured with anintegrating sphere by measuring light from a light source passing andscattering on a specimen, using a spectrophotometer (Hitachispectrophotometer, Model U-3900H manufactured by HitachiHigh-Technologies Corporation). In the measurement, the transmittancefor light of 700 nm wavelength was determined after measuringtransmittance in a wavelength region of 300 to 750 nm. For themeasurement, a disc-shaped zirconia sintered body having mirror polishedsurfaces and measuring 15 mm in diameter and 0.5 mm in thickness wasused as a specimen.

(6) Linear Light Transmittance (1.0 mm Thickness)

The linear light transmittance of zirconia sintered body through athickness of 1.0 mm was measured with an integrating sphere by measuringlight from a light source passing and scattering on a specimen, using aturbidimeter (Haze Meter NDH 4000 manufactured by Nippon DenshokuIndustries Co., Ltd.). In the measurement, the linear lighttransmittance was measured in compliance with ISO 13468-1:1996 and JIS K7361-1:1997, and the haze was measured in compliance with ISO14782-1:1999 and JIS K 7136:2000. For the measurement, a disc-shapedzirconia sintered body having mirror polished surfaces and measuring 15mm in diameter and 1.0 mm in thickness was used as a specimen.

(7) Fraction of Cubic Crystal System

The fraction of the cubic crystal system in zirconia sintered body wasdetermined by crystal phase analysis. Specifically, the fraction of thecubic crystal was determined by X-ray diffraction (XRD) analysis of amirror finished surface portion of the zirconia sintered body, using thefollowing formula.

f _(c)=100×I _(c)/(I _(m) +I _(t) +I _(c))

Here, f_(c) represents the fraction (%) of the cubic crystal system inthe zirconia sintered body, I_(m) represents the height of a peak (apeak attributed to the (11-1) plane of a monoclinic crystal system) near2θ=28 degrees, It represents the height of a peak (a peak attributed tothe (111) plane of a tetragonal crystal system) near 2θ=30 degrees, andI_(c) represents the height of a peak (a peak attributed to the (111)plane of the cubic crystal system) near 2θ=30 degrees. For themeasurement, disc-shaped zirconia sintered bodies of Examples andComparative Examples were used as specimens.

(8) Fraction of Monoclinic Crystal System After Hot-Water Treatment

The fraction of monoclinic crystal system with respect to tetragonalcrystal system and cubic crystal system after the zirconia sintered bodyis immersed in 180° C. hot water for 5 hours was determined by mirrorpolishing a surface of the zirconia sintered body, and measuring themirror polished surface portion by X-ray diffraction (XRD) analysisafter the zirconia sintered body was immersed in 180° C. hot water for 5hours, using the following formula.

f _(m)=100×I _(m)/(I _(t+c))

Here, f_(m) represents the fraction (%) of the monoclinic crystal systemwith respect to the tetragonal crystal system and the cubic crystalsystem in the zirconia sintered body immersed in 180° C. hot water for 5hours, I_(m) represents the height of a peak (a peak attributed to the(11-1) plane of the monoclinic crystal) near 2θ=28 degrees, and I_(t+c)represents the height of a peak (a peak attributed to the mixed phase ofthe (111) plane of the tetragonal crystal system and the (111) plane ofthe cubic crystal system) near 2θ=30 degrees. For the measurement,disc-shaped zirconia sintered bodies of Examples and ComparativeExamples were used as specimens.

(9) Appearance of Zirconia Sintered Body

The appearance (color) of zirconia sintered body was evaluated by visualinspection.

(10) Fluorescence of Zirconia Sintered Body

For evaluation of the fluorescence of zirconia sintered body, thepresence or absence of fluorescence under UV light was determined byvisual inspection.

(11) ΔL*(W−B) of Zirconia Molded Body and Zirconia Pre-Sintered Body

The ΔL*(W−B) of zirconia molded body and zirconia pre-sintered bodythrough a thickness of 1.5 mm was measured with a spectrophotometer.Specifically, the ΔL*(W−B) was measured with a spectrophotometer(CM-3610A manufactured by Konica Minolta Japan, Inc.), and calculatedwith color management software SpectraMagic NX ver. 2.5 manufactured byKonica Minolta Co., Ltd. In the measurement, the ΔL*(W−B) was determinedby using F11 as a light source and measuring reflected light. For themeasurement, disc-shaped zirconia molded body and zirconia pre-sinteredbody each having mirror polished surfaces and measuring 20 mm indiameter and 1.5 mm in thickness were used as specimens.

Example 1

A 1.0-L mixed aqueous solution of 0.62 mol/L zirconium oxychloride and0.038 mol/L yttrium chloride, and 0.5 L of a 1.9 mol/L aqueous solutionof sodium hydroxide were separately prepared.

After pouring 1.0 L of purified water into a precipitation vessel, themixed aqueous solution and the sodium hydroxide aqueous solution weresimultaneously poured into the vessel to obtain a slurry throughcoprecipitation of zirconium oxychloride and yttrium chloride. After theslurry was filtered and washed, 22.2 g of acetic acid was added to theslurry and a hydrothermal treatment was conducted at 200° C. for 3hours. The obtained slurry was subjected to centrifugal filtration witha membrane filter having a pore diameter of 100 nm, and purified waterwas added so that a solid content (a concentration of zirconia andyttria) was 5.0 mass %, to produce a zirconia slurry from which coarseparticles have been removed. The zirconia particles contained in thezirconia slurry had an average primary particle diameter of 17 nm, andwere not confirmed to include zirconia particles having a particlediameter of more than 100 nm.

The zirconia slurry was poured as a molding slurry into a plaster moldand allowed to stand for 2 weeks at room temperature, and then wassubjected to cold isostatic pressing (CIP) (170 MPa pressure) to obtainzirconia molded bodies of increased density. The plaster mold wasprepared so that a molded body before being subjected to CIP had a plateshape measuring 25 mm×25 mm×5 mm in size and a disc shape measuring 20mm in diameter and 2.5 mm in thickness. The plaster mold was prepared bymixing water into a plaster (Noritake Dental Plaster manufactured byKuraray Noritake Dental Inc.) in a proportion of 50 mass %. The zirconiamolded body was pre-sintered at 500° C. for 2 hours under ordinarypressure to obtain a zirconia pre-sintered body. The zirconiapre-sintered body was sintered at 1,100° C. for 2 hours under ordinarypressure to obtain a zirconia sintered body containing 3 mol % yttria.The obtained zirconia sintered body was white in color. The measurementresults are presented in Table 1.

The zirconia pre-sintered body produced in the manner described abovewas cut into shapes of crowns for maxillary central incisor andmandibular first molar using a milling device (Katana H-18 manufacturedby Kuraray Noritake Dental Inc.). These were then sintered at 1,100° C.for 2 hours under ordinary pressure to obtain crown-shaped dentalprostheses.

Example 2

A zirconia slurry was produced in the same manner as in Example 1,except that a mixed aqueous solution of 1.0 L containing 0.62 mol/Lzirconium oxychloride and 0.066 mol/L yttrium chloride was used in placeof the mixed aqueous solution used in Example 1. The zirconia particlescontained in the zirconia slurry had an average primary particlediameter of 18 nm, and included 0.35 mass % zirconia particles having aparticle diameter of more than 100 nm.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 1, except that the zirconia slurry prepared abovewas used as a molding slurry. The obtained zirconia sintered body waswhite in color. The measurement results are presented in Table 1.

Example 3

A zirconia slurry was produced in the same manner as in Example 1,except that a mixed aqueous solution of 1.0 L containing 0.62 mol/Lzirconium oxychloride and 0.108 mol/L yttrium chloride was used in placeof the mixed aqueous solution used in Example 1. The zirconia particlescontained in the zirconia slurry had an average primary particlediameter of 17 nm, and included 0.15 mass % zirconia particles having aparticle diameter of more than 100 nm.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 8 mol % yttria were obtained in the samemanner as in Example 1, except that the zirconia slurry prepared abovewas used as a molding slurry. The obtained zirconia sintered body waswhite in color. The measurement results are presented in Table 1.

Example 4

A molding slurry containing zirconia particles and a fluorescent agentwas prepared by adding a dilute nitric acid solution of bismuth nitrateto the zirconia slurry prepared in Example 2 (having an average primaryparticle diameter of 18 nm and including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm) so that the resultingmixture had a concentration of 0.02 mass % in terms of an oxide ofbismuth (Bi₂O₃) relative to the mass of zirconia.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 1, except that the molding slurry prepared abovewas used. The zirconia sintered body obtained was white in color, andhad fluorescence. The measurement results are presented in Table 1.

Example 5

A molding slurry containing zirconia particles and a colorant wasprepared by adding an aqueous solution of nickel(II) nitrate to thezirconia slurry prepared in Example 2 (having an average primaryparticle diameter of 18 nm and including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm) so that the resultingmixture had a concentration of 0.02 mass % in terms of an oxide ofnickel(II) (NiO) relative to the mass of zirconia.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 1, except that the molding slurry prepared abovewas used. The zirconia sintered body obtained was red in color. Themeasurement results are presented in Table 1.

Comparative Example 1

By uniaxial pressing, a zirconia particle powder TZ-3Y (manufactured byTosoh Corporation, yttria content of 3 mol %, average primary particlediameter of 30 nm) was formed into a plate shape measuring 25 mm×25 mm×5mm in size, and a disc shape measuring 20 mm in diameter and 2.5 mm inthickness. These were subjected to cold isostatic pressing (CIP) (170MPa pressure) to obtain zirconia molded bodies of increased density.These zirconia molded bodies were pre-sintered at 500° C. for 2 hoursunder ordinary pressure to obtain zirconia pre-sintered bodies. Thezirconia pre-sintered bodies were sintered at 1,100° C. for 2 hoursunder ordinary pressure to obtain a zirconia sintered body containing 3mol % yttria. The obtained zirconia sintered body was white in color.The measurement results are presented in Table 1.

Comparative Example 2

The zirconia molded body produced in Comparative Example 1 waspre-sintered at 500° C. for 2 hours under ordinary pressure to obtainzirconia pre-sintered bodies. The zirconia pre-sintered bodies weresintered at 1,500° C. for 2 hours under ordinary pressure to obtain azirconia sintered body containing 3 mol % yttria. The obtained zirconiasintered body was white in color. The measurement results are presentedin Table 1.

Comparative Example 3

By uniaxial pressing, a zirconia particle powder TZ-8YS (manufactured byTosoh Corporation, yttria content of 8 mol %, average primary particlediameter of 300 nm) was formed into a plate shape measuring 25 mm×25mm×5 mm in size, and a disc shape measuring 20 mm in diameter and 2.5 mmin thickness. These were subjected to cold isostatic pressing (CIP) (170MPa pressure) to obtain zirconia molded bodies of increased density.These zirconia molded bodies were pre-sintered at 500° C. for 2 hoursunder ordinary pressure to obtain zirconia pre-sintered bodies. Thezirconia pre-sintered bodies were sintered at 1,500° C. for 2 hoursunder ordinary pressure to obtain a zirconia sintered body containing 8mol % yttria. The obtained zirconia sintered body was white in color.The measurement results are presented in Table 1.

Comparative Example 4

A 1.0-L mixed aqueous solution of 0.62 mol/L zirconium oxychloride and0.066 mol/L yttrium chloride, and 0.5 L of a 1.9 mol/L aqueous solutionof sodium hydroxide were separately prepared.

After pouring 1.0 L of purified water into a precipitation vessel, themixed aqueous solution and the sodium hydroxide aqueous solution weresimultaneously poured into the vessel to obtain a slurry throughcoprecipitation of zirconium oxychloride and yttrium chloride.

After the slurry was filtered and washed, 22.2 g of acetic acid wasadded to the slurry and a hydrothermal treatment was conducted at 200°C. for 3 hours. Purified water was added to produce a zirconia slurryhaving a solid content of 5.0 mass % (a concentration of zirconia andyttria). The zirconia particles contained in the zirconia slurry had anaverage primary particle diameter of 19 nm, and included 5.3 mass %zirconia particles having a particle diameter of more than 100 nm.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 1, except that the zirconia slurry obtained abovewas used as a molding slurry. The obtained zirconia sintered body waswhite in color. The measurement results are presented in Table 1.

TABLE 1 Comparative Example Example 1 2 3 4 5 1 2 3 4 Content offluorescent mass % — — — 0.02 — — — — — agent (*1) Content of colorantmass % — — — — 0.02 — — — — (*1) Content of yttria (*2) mol % 3 5 8 5 53 3 8 5 Zirconia molded body — 8.3 14.3 16.6 13.3 13.6 0 0 0 3.3ΔL*(W-B) Zirconia pre-sintered body — 7.2 13.6 15.8 12.7 12.9 0 0 0 2.5ΔL*(W-B) Zirconia sintered body nm 80 83 91 84 84 107 520 608 92 Crystalgrain size Three-point flexural MPa 1021 840 603 802 811 221 1172 350822 strength Light transmittance % 42 48 57 41 44 0 21 32 43 (700 nmwavelength, 0.5 mm thickness) Linear light % 1.8 9.2 14.5 6.4 7.0 0 0.40.5 0.4 transmittance (1.0 mm thickness) Fraction of cubic % 32 100 100100 100 0 31 100 100 crystal Fraction of monoclinic % 0 0 0 0 0 0 0 0 0crystal after hot-water treatment (*1) Content relative to the mass ofzirconia (the content is in terms of an oxide of metallic element) (*2)Fraction of the number of moles of yttria with respect to the totalnumber of moles of zirconia and yttria

Example 6

To the zirconia slurry prepared in Example 2 (having an average primaryparticle diameter of 18 nm and including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm), tetramethylammoniumhydroxide was added as a pH adjuster and triammonium citrate was addedas a dispersant. Thereafter, agarose was added as a gelatinizer whilestirring the mixture under heat to produce a molding slurry containingzirconia particles, a pH adjuster, a dispersant, and a gelatinizer.

The molding slurry was poured into a polypropylene mold, and dried atroom temperature for 16 days to obtain a zirconia molded body. Thezirconia molded body was pre-sintered at 500° C. for 2 hours underordinary pressure to obtain a zirconia pre-sintered body. The zirconiapre-sintered body was sintered at 1,100° C. for 2 hours under ordinarypressure to obtain a zirconia sintered body containing 5 mol % yttria.The obtained zirconia sintered body was white in color. The measurementresults are presented in Table 2.

Example 7

On the zirconia slurry prepared in Example 2 (having an average primaryparticle diameter of 18 nm and including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm), a dispersion mediumreplacement procedure was conducted in which 50 parts by mass of2-ethoxyethanol was added, and concentrated to make the total amount 100parts by mass, using a rotary evaporator. The dispersion mediumreplacement procedure was repeated 4 times to obtain a2-ethoxyethanol-replaced slurry. The 2-ethoxyethanol-replaced slurry hada residual moisture content of 0.05 mass % as measured with a KarlFisher moisture content meter.

The 2-ethoxyethanol-replaced slurry was dried with a spray drier (B-290manufactured by Buchi Labortechnik AG, Japan) at a feed rate of 5 mL/minand inlet and outlet temperatures of 150° C. and 100° C., respectively,to obtain a powder containing zirconia particles.

By uniaxial pressing, the powder was formed into a plate shape measuring25 mm×25 mm×5 mm in size, and a disc shape measuring 20 mm in diameterand 2.5 mm in thickness. These were then subjected to cold isostaticpressing (CIP) (170 MPa pressure) to obtain zirconia molded bodies ofincreased density. These zirconia molded bodies were pre-sintered at500° C. for 2 hours under ordinary pressure to obtain zirconiapre-sintered bodies. The zirconia pre-sintered bodies were sintered at1,100° C. for 2 hours under ordinary pressure to obtain a zirconiasintered body containing 5 mol % yttria. The obtained zirconia sinteredbody was white in color. The measurement results are presented in Table2.

The zirconia pre-sintered body produced in the manner described abovewas cut into shapes of crowns for maxillary central incisor andmandibular first molar using a milling device (Katana H-18 manufacturedby Kuraray Noritake Dental Inc.). These were then sintered at 1,100° C.for 2 hours under ordinary pressure to obtain crown-shaped dentalprostheses.

Example 8

To the zirconia slurry prepared in Example 2 (having an average primaryparticle diameter of 18 nm and including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm), isopropanol was addedin 9 times the volume of the zirconia slurry. The mixture was placed ina centrifuge tube, thoroughly mixed, and centrifuged at 4,000 rpm for 10minutes. After confirming sedimentation of a white substance, thesupernatant was removed, and isopropanol was added again. The mixturewas thoroughly mixed, and centrifuged at 4,000 rpm for 10 minutes. Thesupernatant was removed after confirming sedimentation of a whitesubstance, and methanol was added to make the volume of the mixture thesame as the volume of the zirconia slurry used. The mixture was thenthoroughly mixed to obtain a methanol-replaced slurry. Themethanol-replaced slurry had a residual moisture content of 0.08 mass %as measured with a Karl Fisher moisture content meter.

The methanol-replaced slurry produced was subjected to supercriticaldrying with a supercritical drier using the following procedure.Specifically, the methanol-replaced slurry was placed in a pressurevessel, and the pressure vessel was coupled to a supercritical carbondioxide extraction device. After checking that there is no pressureleak, the pressure vessel, with a preheating tube, was immersed in awater bath that had been heated to 60° C. The slurry was then allowed tostand for 10 minutes to stabilize after being heated to 80° C. andpressurized to 25 MPa. Thereafter, carbon dioxide and entrainer methanolwere introduced under predetermined conditions (temperature: 80° C.,pressure: 25 MPa, carbon dioxide flow rate: 10 mL/min, entrainer(methanol) flow rate: 1.5 mL/min). The feeding of methanol wasdiscontinued after an elapsed time period of 2 hours, without stoppingthe carbon dioxide feed. After 2 hours with the sole supply of carbondioxide, the feeding of carbon dioxide was stopped, and the pressure wasgradually brought back to ordinary pressure from 25 MPa over a timeperiod of about 20 minutes at a maintained temperature of 80° C. Thepressure vessel was then taken out of the water bath, and cooled toordinary temperature. The processed specimen was collected by openingthe container, and a powder containing zirconia particles was obtained.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 7, except that the powder obtained above was used.The obtained zirconia sintered body was white in color. The measurementresults are presented in Table 2.

Example 9

To the zirconia slurry prepared in Example 2 (having an average primaryparticle diameter of 18 nm and including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm), isopropanol was addedin 9 times the volume of the zirconia slurry. The mixture was placed ina centrifuge tube, thoroughly mixed, and centrifuged at 4,000 rpm for 10minutes. After confirming sedimentation of a white substance, thesupernatant was removed, and isopropanol was added again. The mixturewas thoroughly mixed, and centrifuged at 4,000 rpm for 10 minutes. Thesupernatant was removed after confirming sedimentation of a whitesubstance, and tert-butyl alcohol was added to make the volume of themixture the same as the volume of the zirconia slurry used. The mixturewas then thoroughly mixed to obtain a tert-butyl alcohol-replacedslurry. The tert-butyl alcohol-replaced slurry had a residual moisturecontent of 0.05 mass % as measured with a Karl Fisher moisture contentmeter.

The tert-butyl alcohol-replaced slurry was transferred to an aluminumvat, and immersed in liquid nitrogen in a separately prepared Dewarflask to freeze. The frozen tert-butyl alcohol-replaced slurry wasallowed to stand in a freeze drier that had been precooled to −40° C.The pressure inside the freeze drier was then reduced to 130 Pa or lesswith a vacuum pump to bring the temperature inside the freeze drier to−10° C. The internal temperature of the freeze drier was confirmed byinserting temperature sensors inside and outside of the aluminum vat.After the temperature inside the freeze drier had stabilized at −10° C.for 72 hours, the temperature difference inside and outside of thealuminum vat was confirmed to be within 5° C., and the temperatureinside the freeze drier was brought to 30° C. After being allowed tostand for 24 hours, the inside of the freeze drier was released from thereduced pressure to obtain a powder containing zirconia particles.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 7, except that the powder obtained above was used.The obtained zirconia sintered body was white in color. The measurementresults are presented in Table 2.

Example 10

A molding slurry containing zirconia particles and a fluorescent agentwas prepared by adding a dilute nitric acid solution of bismuth nitrateto the zirconia slurry prepared in Example 1 (having an average primaryparticle diameter of 17 nm, no confirmation of inclusion of zirconiaparticles having a particle diameter of more than 100 nm) so that theresulting mixture had a concentration of 0.02 mass % in terms of anoxide of bismuth (Bi₂O₃) relative to the mass of zirconia.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 3 mol % yttria were obtained in the samemanner as in Example 1, except that the molding slurry obtained abovewas used. The zirconia sintered body obtained was white in color, andhad fluorescence. The measurement results are presented in Table 2.

Example 11

A molding slurry containing zirconia particles and a fluorescent agentwas prepared by adding a dilute nitric acid solution of bismuth nitrateto the zirconia slurry prepared in Example 3 (having an average primaryparticle diameter of 17 nm and including 0.15 mass % zirconia particleshaving a particle diameter of more than 100 nm) so that the resultingmixture had a concentration of 0.02 mass % in terms of an oxide ofbismuth (Bi₂O₃) relative to the mass of zirconia.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 8 mol % yttria were obtained in the samemanner as in Example 3, except that the slurry obtained above was usedas a molding slurry. The zirconia sintered body obtained was white incolor, and had fluorescence. The measurement results are presented inTable 2.

Example 12

To the zirconia slurry prepared in Example 4 (having an average primaryparticle diameter of 18 nm, including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm, and having added theretoa dilute nitric acid solution of bismuth so that the resulting mixturehad a concentration of 0.02 mass % in terms of an oxide of bismuth(Bi₂O₃) relative to the mass of zirconia), tetramethylammonium hydroxidewas added as a pH adjuster and triammonium citrate was added as adispersant. Thereafter, agarose was added as a gelatinizer whilestirring the mixture under heat to produce a molding slurry containingzirconia particles, a fluorescent agent, a pH adjuster, a dispersant,and a gelatinizer.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 6, except that the molding slurry obtained abovewas used. The zirconia sintered body obtained was white in color, andhad fluorescence. The measurement results are presented in Table 2.

Example 13

On the zirconia slurry prepared in Example 4 (having an average primaryparticle diameter of 18 nm, including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm, and having added theretoa dilute nitric acid solution of bismuth so that the resulting mixturehad a concentration of 0.02 mass % in terms of an oxide of bismuth(Bi₂O₃) relative to the mass of zirconia), a dispersion mediumreplacement procedure was conducted in which 50 parts by mass of2-ethoxyethanol was added, and concentrated to make the total amount 100parts by mass, using a rotary evaporator. The dispersion mediumreplacement procedure was repeated 4 times to obtain a2-ethoxyethanol-replaced slurry. The 2-ethoxyethanol-replaced slurry hada residual moisture content of 0.07 mass % as measured with a KarlFisher moisture content meter.

The 2-ethoxyethanol-replaced slurry was dried with a spray drier (B-290manufactured by Buchi Labortechnik AG, Japan) at a feed rate of 5 mL/minand inlet and outlet temperatures of 150° C. and 100° C., respectively,to obtain a powder containing zirconia particles and a fluorescentagent.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 7, except that the powder obtained above was used.The zirconia sintered body obtained was white in color, and hadfluorescence. The measurement results are presented in Table 2.

The zirconia pre-sintered body produced in the manner described abovewas cut into shapes of crowns for maxillary central incisor andmandibular first molar using a milling device (Katana H-18 manufacturedby Kuraray Noritake Dental Inc.). These were then sintered at 1,100° C.for 2 hours under ordinary pressure to obtain crown-shaped dentalprostheses. The crown-shaped zirconia sintered body obtained hadfluorescence.

Example 14

To the zirconia slurry prepared in Example 4 (having an average primaryparticle diameter of 18 nm, including 0.35 mass % zirconia particleshaving a particle diameter of more than 100 nm, and having added theretoa dilute nitric acid solution of bismuth so that the resulting mixturehad a concentration of 0.02 mass % in terms of an oxide of bismuth(Bi₂O₃) relative to the mass of zirconia), isopropanol was added in 9times the volume of the zirconia slurry. The mixture was placed in acentrifuge tube, thoroughly mixed, and centrifuged at 4,000 rpm for 10minutes. After confirming sedimentation of a white substance, thesupernatant was removed, and isopropanol was added again. The mixturewas thoroughly mixed, and centrifuged at 4,000 rpm for 10 minutes. Thesupernatant was removed after confirming sedimentation of a whitesubstance, and methanol was added to make the volume of the mixture thesame as the volume of the zirconia slurry used. The mixture was thenthoroughly mixed to obtain a methanol-replaced slurry. Themethanol-replaced slurry had a residual moisture content of 0.06 mass %as measured with a Karl Fisher moisture content meter. A powdercontaining zirconia particles and a fluorescent agent was obtained inthe same manner as in Example 8, except that the methanol-replacedslurry was used.

A zirconia molded body, a zirconia pre-sintered body, and a zirconiasintered body each containing 5 mol % yttria were obtained in the samemanner as in Example 8, except that the powder obtained above was used.The zirconia sintered body obtained was white in color, and hadfluorescence. The measurement results are presented in Table 2.

The zirconia pre-sintered body produced in the manner described abovewas cut into shapes of crowns for maxillary central incisor andmandibular first molar using a milling device (Katana H-18 manufacturedby Kuraray Noritake Dental Inc.). These were then sintered at 1,100° C.for 2 hours under ordinary pressure to obtain crown-shaped dentalprostheses. The crown-shaped zirconia sintered body obtained hadfluorescence.

TABLE 2 Example 6 7 8 9 10 11 12 13 14 Content of fluorescent mass — — —— 0.02 0.02 0.02 0.02 0.02 agent (*1) % Content of colorant mass — — — —— — — — — (*1) % Content of yttria (*2) mol % 5 5 5 5 3 8 5 5 5 Zirconiamolded body — 15.6 13.4 15.4 13.7 7.9 16.1 15.1 13.1 14.9 ΔL*(W-B)Zirconia pre-sintered body — 14.3 12.8 14.0 13.2 6.6 15.2 13.2 12.5 13.3ΔL*(W-B) Zirconia sintered body nm 80 86 81 85 81 93 82 88 82 Crystalgrain size Three-point MPa 871 801 862 812 1002 581 855 767 849 flexuralstrength Light transmittance % 50 43 50 43 40 51 46 41 47 (700 nmwavelength, 0.5 mm thickness) Linear light % 11.3 7.1 10.2 7.3 1.6 13.210.1 6.1 9.6 transmittance (1.0 mm thickness) Fraction of % 100 100 100100 34 100 100 100 100 cubic crystal Fraction of monoclinic % 0 0 0 0 00 0 0 0 crystal after hot-water treatment (*1) Content relative to themass of zirconia (the content is in terms of an oxide of metallicelement) (*2) Fraction of the number of moles of yttria with respect tothe total number of moles of zirconia and yttria

1. A zirconia molded body comprising zirconia particles comprising 2.0to 9.0 mol % yttria, having an average primary particle diameter of 60nm or less, and including 0.5 mass % or less zirconia particles having aparticle diameter of more than 100 nm, wherein the zirconia molded bodyhas ΔL*(W−B) of 5 or more through a thickness of 1.5 mm.
 2. The zirconiamolded body according to claim 1, wherein the zirconia molded body has athree-point flexural strength of 500 MPa or more after being sintered at900 to 1200° C. under ordinary pressure.
 3. The zirconia molded body ofclaim 1, wherein the zirconia molded body has a transmittance of 40% ormore for light of 700 nm wavelength through a thickness of 0.5 mm afterbeing sintered at 900 to 1200° C. under ordinary pressure.
 4. Thezirconia molded body of claim 1, wherein the zirconia molded bodycomprises a monoclinic crystal system in a fraction of 5% or less withrespect to a tetragonal crystal system and a cubic crystal system afterbeing sintered at 900 to 1200° C. under ordinary pressure and thenimmersed in 180° C. hot water for 5 hours.
 5. The zirconia molded bodyof claim 1, wherein the zirconia molded body has ΔL*(W−B) of 5 or morethrough a thickness of 1.5 mm after being sintered at 200 to 800° C. 6.A zirconia pre-sintered body comprising 2.0 to 9.0 mol % yttria, whereinthe zirconia pre-sintered body has ΔL*(W−B) of 5 or more through athickness of 1.5 mm.
 7. The zirconia pre-sintered body according toclaim 6, wherein the zirconia pre-sintered body has a three-pointflexural strength of 500 MPa or more after being sintered at 900 to1200° C. under ordinary pressure.
 8. The zirconia pre-sintered body ofclaim 6, wherein the zirconia pre-sintered body has a transmittance of40% or more for light of 700 nm wavelength through a thickness of 0.5 mmafter being sintered at 900 to 1200° C. under ordinary pressure.
 9. Thezirconia pre-sintered body of claim 6, wherein the zirconia pre-sinteredbody comprises a monoclinic crystal system in a fraction of 5% or lesswith respect to a tetragonal crystal system and a cubic crystal systemafter being sintered at 900 to 1200° C. under ordinary pressure and thenimmersed in 180° C. hot water for 5 hours.
 10. A method for producing azirconia pre-sintered body, wherein the method uses the zirconia moldedbody of claim
 1. 11. The method according to claim 10, comprising a stepof pre-sintering the zirconia molded body of claim 1 at 200 to 800° C.12. A zirconia sintered body comprising: a fluorescent agent; and 2.0 to9.0 mol % yttria, wherein the zirconia sintered body has a linear lighttransmittance of 1% or more through a thickness of 1.0 mm.
 13. Thezirconia sintered body according to claim 12, wherein the zirconiasintered body has a three-point flexural strength of 500 MPa or more.14. The zirconia sintered body of claim 12, wherein the zirconiasintered body has a transmittance of 40% or more for light of 700 nmwavelength through a thickness of 0.5 mm.
 15. The zirconia sintered bodyof claim 12, wherein the zirconia sintered body comprises a monocliniccrystal system in a fraction of 5% or less with respect to a tetragonalcrystal system and a cubic crystal system after being immersed in 180°C. hot water for 5 hours.
 16. A method for producing a zirconia sinteredbody, wherein the method uses the zirconia molded body of claim
 1. 17.The method according to claim 16, comprising a step of sintering thezirconia molded body at 900 to 1200° C. under ordinary pressure.
 18. Amethod for producing a zirconia sintered body, wherein the method usesthe zirconia pre-sintered body of claim
 6. 19. The method according toclaim 18, comprising a step of sintering the zirconia pre-sintered bodyat 900 to 1200° C. under ordinary pressure.